题目内容
The coastlines on the two sides of the Atlantic Ocean present a notable parallelism: the easternmost region of Brazil, in Pernambuco, has a convexity that corresponds almost perfectly with the concavity of the African Gulf of Guinea, while the contours of the African coastline between Rio de Oro and Liberia would, by the same approximation, match those of the Caribbean Sea. Similar correspondences are also observed in many other regions of the earth. This observation began to awaken scientific interest about sixty years ago, when Alfred Wegener, a professor at the University of Hamburg, used it as a basis for formulating a revolutionary theory in geological science. According to Wegener, there was originally only one continent or landmass, which he called Pangea. Inasmuch as continental masses are lighter than tile base on which they rest, he reasoned, they must float on the substratum of igneous rock, known as sima, as ice floes float on the sea. Then why, he asked, might continents not be subject to drifting The rotation of the globe and other forces, he thought, had caused the cracking and, finally, the breaking apart of the original Pangea, along an extensive line represented today by the longitudinal submerged mountain range in the center of the Atlantic. While Africa seems to have remained static, the Americas apparently drifted toward the west until they reached their present position after more than 100 million years. Although the phenomenon seems fantastic, accustomed as we are to the concept of the rigidity and immobility of the continents, on the basis of the distance that separates them it is possible to calculate that the continental drift would have been no greater than two inches per year. The submerged mountain range in the Atlantic ______.
查看答案
搜索结果不匹配？点我反馈
更多问题
Directions: There are 5 reading passages in this part. Each passage is followed by some questions or unfinished statements. For each of them there are four choices marked A, B, C, and D. You should decide on the best choice and mark your answer on the ANSWER SHEET by blackening the corresponding letter in the brackets. A man-made chemical that attracts male gypsy moths by duplicating the natural attractant of female gypsy moths has been patented as No. 3,018,219. Dr. Martin Jacobson of Silver Spring, Md., assigned patent rights to the U. S. Government as represented by the Secretary of Agriculture. The chemical can be used to detect gypsy moth infestations, as well as to control the insects. The gypsy moth does serious damage to forest and shade trees in New England and eastern New York State. The caterpillars, or larvae, of gypsy moths eat the leaves of trees, often causing death by a single attack. Losses of hardwood trees have been estimated at tens of millions of dollars from a 20-year study. Gypsy moths were prevented from spreading to other U. S. forest areas by using the natural attractant of the female to detect infestations, then spraying with chemicals such as DDT to kill the insects. Since the lure could previously be obtained only by clipping the last two abdominal segments of the virgin female moth, extracting the segments with benzene and then processing to stabilize the chemical, the procedure was expensive. Another difficulty was that, as the gypsy moth population declined, it became increasingly hard to obtain the females needed for lure production. Dr. Jacobson overcame both these difficulties by discovering a synthetic method for making the female’s attractant chemical. The chemical is known as 12-acetoxy-l-hydroxycis-9- octadecene. It is so potent that the fraction of a drop produced by the female is 200,000 times more than the amount needed to catch a mate. The synthetic chemical is also very powerful--it works in amounts about equivalent to one drop in a box car. The flightless female gypsy moth mates only once a year and, as soon as she does, an enzyme switches off production of the sex attractant. The winged male, however, call mate several times and it is because of this that the chemical is being used for pest control. By using a mixture of attractant and DDT in traps lined with a sticky substance, enough males can be caught to reduce the gypsy moth population substantially. Dr. Jacobson’s chemical works by ______.
Directions: There are 5 reading passages in this part. Each passage is followed by some questions or unfinished statements. For each of them there are four choices marked A, B, C, and D. You should decide on the best choice and mark your answer on the ANSWER SHEET by blackening the corresponding letter in the brackets. A man-made chemical that attracts male gypsy moths by duplicating the natural attractant of female gypsy moths has been patented as No. 3,018,219. Dr. Martin Jacobson of Silver Spring, Md., assigned patent rights to the U. S. Government as represented by the Secretary of Agriculture. The chemical can be used to detect gypsy moth infestations, as well as to control the insects. The gypsy moth does serious damage to forest and shade trees in New England and eastern New York State. The caterpillars, or larvae, of gypsy moths eat the leaves of trees, often causing death by a single attack. Losses of hardwood trees have been estimated at tens of millions of dollars from a 20-year study. Gypsy moths were prevented from spreading to other U. S. forest areas by using the natural attractant of the female to detect infestations, then spraying with chemicals such as DDT to kill the insects. Since the lure could previously be obtained only by clipping the last two abdominal segments of the virgin female moth, extracting the segments with benzene and then processing to stabilize the chemical, the procedure was expensive. Another difficulty was that, as the gypsy moth population declined, it became increasingly hard to obtain the females needed for lure production. Dr. Jacobson overcame both these difficulties by discovering a synthetic method for making the female’s attractant chemical. The chemical is known as 12-acetoxy-l-hydroxycis-9- octadecene. It is so potent that the fraction of a drop produced by the female is 200,000 times more than the amount needed to catch a mate. The synthetic chemical is also very powerful--it works in amounts about equivalent to one drop in a box car. The flightless female gypsy moth mates only once a year and, as soon as she does, an enzyme switches off production of the sex attractant. The winged male, however, call mate several times and it is because of this that the chemical is being used for pest control. By using a mixture of attractant and DDT in traps lined with a sticky substance, enough males can be caught to reduce the gypsy moth population substantially. Prior to Dr. Jacobson’s synthetic drug, scientists found difficulty in controlling the pest because ______.
Directions: In this part, you are required to write a composition entitled Migrant Farmer Workers in China in no less than 200 words. Your composition should be based on the following outline: 1. An important role China’s migrant farmer workers play in the construction of our socialist modernization. 2. The problems they are confronted with. 3. Our government’s concern for them.
Directions: There are 5 reading passages in this part. Each passage is followed by some questions or unfinished statements. For each of them there are four choices marked A, B, C, and D. You should decide on the best choice and mark your answer on the ANSWER SHEET by blackening the corresponding letter in the brackets. A man-made chemical that attracts male gypsy moths by duplicating the natural attractant of female gypsy moths has been patented as No. 3,018,219. Dr. Martin Jacobson of Silver Spring, Md., assigned patent rights to the U. S. Government as represented by the Secretary of Agriculture. The chemical can be used to detect gypsy moth infestations, as well as to control the insects. The gypsy moth does serious damage to forest and shade trees in New England and eastern New York State. The caterpillars, or larvae, of gypsy moths eat the leaves of trees, often causing death by a single attack. Losses of hardwood trees have been estimated at tens of millions of dollars from a 20-year study. Gypsy moths were prevented from spreading to other U. S. forest areas by using the natural attractant of the female to detect infestations, then spraying with chemicals such as DDT to kill the insects. Since the lure could previously be obtained only by clipping the last two abdominal segments of the virgin female moth, extracting the segments with benzene and then processing to stabilize the chemical, the procedure was expensive. Another difficulty was that, as the gypsy moth population declined, it became increasingly hard to obtain the females needed for lure production. Dr. Jacobson overcame both these difficulties by discovering a synthetic method for making the female’s attractant chemical. The chemical is known as 12-acetoxy-l-hydroxycis-9- octadecene. It is so potent that the fraction of a drop produced by the female is 200,000 times more than the amount needed to catch a mate. The synthetic chemical is also very powerful--it works in amounts about equivalent to one drop in a box car. The flightless female gypsy moth mates only once a year and, as soon as she does, an enzyme switches off production of the sex attractant. The winged male, however, call mate several times and it is because of this that the chemical is being used for pest control. By using a mixture of attractant and DDT in traps lined with a sticky substance, enough males can be caught to reduce the gypsy moth population substantially. We may assume that Dr. Jacobson assigned patent rights to the United States Government because he ______.
微信支付 
支付宝支付