题目内容
For centuries, explorers have risked their lives venturing into the unknown for reasons of economic benefit and national glory. Following the lunar missions of the early 1970s, Mars now looms as humanity’s next great, unknown land. But with dubious prospects for short-term financial return and with international competition in space a receding memory, it is clear that imperatives other than profit or national pride will have to compel human beings to leave their tracks on the planet’s red surface.With Mars the scientific benefits are perhaps higher than they have ever been. The issue of whether life ever existed on the planet, and whether it persists to this day, has been highlighted by accumulating evidence that Mars once had abundant liquid water and by the controversy over suggestions that fossils of bacteria rode to Earth on a rock ejected from Mars during its early history. A definite answer about life on Mars, past or present, would give researchers invaluable data about the range of conditions under which a planet can generate the complex chemistry that leads to life. The revelation that life arose independently on Mars and on Earth would provide the first concrete clue in one of the deepest mysteries in all of science: how prevalent is life in our galaxyOne of the reasons why the idea of sending people to Mars strikes a chord in so many people is that it is already possible—the U.S. has the money and the fundamental technology needed to do it. More important, recent discoveries about the planet’s environment in the distant past have presented a clear and compelling scientific incentive for sending people: to search for evidence of life. The thesis that liquid water was once stable on Mars has been strengthened by aerial photographs taken last year that showed what appeared to be a drainage channel cut deeply by water flowing for hundreds if not thousands of years.A thorough hunt for any life on Mars that might be hanging on—despite the present deficit of water—would also have to be undertaken by humans, according to some experts. Such life will be hidden and probably tiny. "Finding it will require surveying vast tracts of territory," one expert explains. "It will require the ability to cover long distances and adapt to different conditions." Robots might be up to the task sometime in the distant future, making human explorers redundant, he concedes. But relying on them to survey Mars during periodical missions to the planet would take a very long time— "decades if not centuries," he believes. The aerial photographs taken last year indicate that （）
查看答案
搜索结果不匹配？点我反馈
更多问题
Niagara is an Indian word which means "roaring water". Indeed, the roar of the falling water of Niagara can be heard (1) a distance of 5 kms. Imagine (2) of water flowing over a cliff 90 feet high and you will get an idea of that terrible noise. And (3) tremendous power the Niagara River has! It moves big rocks about and throws them into the boiling water below. (4) ago an old ship without single person on board was put in mid-stream. It sailed down the river (5) a toy boat with great speed. Having reached the fall, the ship dropped into the boiling water, never (6) again. There were some people who wanted to become famous (7) swimming across the most dangerous part of the Niagara River. One of them was Captain Webb who said that he would try to swim cross the Niagara, which (8) crowds of people. On the evening of July 1st, 1893, Captain Webb came up to the river and (9) a plunge. His having jumped into the water (10) many people with horror. Soon, he appeared in the middle of the river. A loud shout went up from the crowd, but a moment later there was (11) silence. The man had disappeared under the water. Thousands of eyes (12) on the river, but the man was drowned. In 1902, a certain Miss Taylor decided to go over the falls in a barrel. There were different kinds of pillows inside the barrel to prevent her from (13) . Having examined the barrel carefully, Miss Taylor got in. The barrel was closed and then (14) into the water. Having reached the falls, it overturned and was shot down by the terrible (15) of the water. When the barrel was finally caught and opened, Miss Taylor came out alive (16) with a frightened look in her eyes. Once a crowd of visitors saw a rope (17) over from one bank of the river to the other. Then they saw a man (18) the rope. The man was an actor, Blondin (19) . He managed to cross Niagara Falls on a tight rope. The people on the bank were surprised at his (20) it so well. Read the following text. Choose the best word (s) for each numbered blank and mark A, B, C or D on ANSWER SHEET 1.7（）
Niagara is an Indian word which means "roaring water". Indeed, the roar of the falling water of Niagara can be heard (1) a distance of 5 kms. Imagine (2) of water flowing over a cliff 90 feet high and you will get an idea of that terrible noise. And (3) tremendous power the Niagara River has! It moves big rocks about and throws them into the boiling water below. (4) ago an old ship without single person on board was put in mid-stream. It sailed down the river (5) a toy boat with great speed. Having reached the fall, the ship dropped into the boiling water, never (6) again. There were some people who wanted to become famous (7) swimming across the most dangerous part of the Niagara River. One of them was Captain Webb who said that he would try to swim cross the Niagara, which (8) crowds of people. On the evening of July 1st, 1893, Captain Webb came up to the river and (9) a plunge. His having jumped into the water (10) many people with horror. Soon, he appeared in the middle of the river. A loud shout went up from the crowd, but a moment later there was (11) silence. The man had disappeared under the water. Thousands of eyes (12) on the river, but the man was drowned. In 1902, a certain Miss Taylor decided to go over the falls in a barrel. There were different kinds of pillows inside the barrel to prevent her from (13) . Having examined the barrel carefully, Miss Taylor got in. The barrel was closed and then (14) into the water. Having reached the falls, it overturned and was shot down by the terrible (15) of the water. When the barrel was finally caught and opened, Miss Taylor came out alive (16) with a frightened look in her eyes. Once a crowd of visitors saw a rope (17) over from one bank of the river to the other. Then they saw a man (18) the rope. The man was an actor, Blondin (19) . He managed to cross Niagara Falls on a tight rope. The people on the bank were surprised at his (20) it so well. Read the following text. Choose the best word (s) for each numbered blank and mark A, B, C or D on ANSWER SHEET 1.6（）
Niagara is an Indian word which means "roaring water". Indeed, the roar of the falling water of Niagara can be heard (1) a distance of 5 kms. Imagine (2) of water flowing over a cliff 90 feet high and you will get an idea of that terrible noise. And (3) tremendous power the Niagara River has! It moves big rocks about and throws them into the boiling water below. (4) ago an old ship without single person on board was put in mid-stream. It sailed down the river (5) a toy boat with great speed. Having reached the fall, the ship dropped into the boiling water, never (6) again. There were some people who wanted to become famous (7) swimming across the most dangerous part of the Niagara River. One of them was Captain Webb who said that he would try to swim cross the Niagara, which (8) crowds of people. On the evening of July 1st, 1893, Captain Webb came up to the river and (9) a plunge. His having jumped into the water (10) many people with horror. Soon, he appeared in the middle of the river. A loud shout went up from the crowd, but a moment later there was (11) silence. The man had disappeared under the water. Thousands of eyes (12) on the river, but the man was drowned. In 1902, a certain Miss Taylor decided to go over the falls in a barrel. There were different kinds of pillows inside the barrel to prevent her from (13) . Having examined the barrel carefully, Miss Taylor got in. The barrel was closed and then (14) into the water. Having reached the falls, it overturned and was shot down by the terrible (15) of the water. When the barrel was finally caught and opened, Miss Taylor came out alive (16) with a frightened look in her eyes. Once a crowd of visitors saw a rope (17) over from one bank of the river to the other. Then they saw a man (18) the rope. The man was an actor, Blondin (19) . He managed to cross Niagara Falls on a tight rope. The people on the bank were surprised at his (20) it so well. Read the following text. Choose the best word (s) for each numbered blank and mark A, B, C or D on ANSWER SHEET 1.17（）
Niagara is an Indian word which means "roaring water". Indeed, the roar of the falling water of Niagara can be heard (1) a distance of 5 kms. Imagine (2) of water flowing over a cliff 90 feet high and you will get an idea of that terrible noise. And (3) tremendous power the Niagara River has! It moves big rocks about and throws them into the boiling water below. (4) ago an old ship without single person on board was put in mid-stream. It sailed down the river (5) a toy boat with great speed. Having reached the fall, the ship dropped into the boiling water, never (6) again. There were some people who wanted to become famous (7) swimming across the most dangerous part of the Niagara River. One of them was Captain Webb who said that he would try to swim cross the Niagara, which (8) crowds of people. On the evening of July 1st, 1893, Captain Webb came up to the river and (9) a plunge. His having jumped into the water (10) many people with horror. Soon, he appeared in the middle of the river. A loud shout went up from the crowd, but a moment later there was (11) silence. The man had disappeared under the water. Thousands of eyes (12) on the river, but the man was drowned. In 1902, a certain Miss Taylor decided to go over the falls in a barrel. There were different kinds of pillows inside the barrel to prevent her from (13) . Having examined the barrel carefully, Miss Taylor got in. The barrel was closed and then (14) into the water. Having reached the falls, it overturned and was shot down by the terrible (15) of the water. When the barrel was finally caught and opened, Miss Taylor came out alive (16) with a frightened look in her eyes. Once a crowd of visitors saw a rope (17) over from one bank of the river to the other. Then they saw a man (18) the rope. The man was an actor, Blondin (19) . He managed to cross Niagara Falls on a tight rope. The people on the bank were surprised at his (20) it so well. Read the following text. Choose the best word (s) for each numbered blank and mark A, B, C or D on ANSWER SHEET 1.12（）
微信支付 
支付宝支付