题目内容
人们可以有意识地控制抽样误差的大小，因为可以调整总体方差。（）
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点估计是直接用一个样本指标估计总体指标的推断方法。（）
抽样误差的概率度是用来测量估计可靠程度的指标。（）
Agriculture is undoubtedly the most important sector in the economies of most non-oil exporting African countries. It (62) about 30% of Africa’s GDP and contributes (63) 50% of the total export value, (64) 70% of the continent’s population depending on the sector for their (65) . Production is subsistence in nature with a high (66) on the rain. The debate on climate change and its impacts on agriculture is (67) very crucial to the very survival of the continent and its people. The continent is particularly (68) to climate change because it includes some of the world’s poorest nations. The climate in Africa is (69) tropical in nature, which is broadly (70) into three main climatic zones: (71) equatorial, dry, and temperate(温带). Within these zones, altitude and other localized (72) also produce distinctive regional climates. Climate change, (73) indicated by prolonged drought is one of the most serious climatic (74) affecting the agricultural sector of the continent. As most of the agriculture activities in African countries hinges on rain fed, any adverse changes in the climate would likely have a (75) effect on the sector in the region. (76) changes in the climate may affect the whole continent, its (77) may vary across the continent. In northeast Africa, more intense dry periods and shorter wet seasons are expected to affect even huge river systems such as the Blue Nile, leading to serious water shortages and (78) consequences to the agriculture and forestry sectors throughout the region. East and Central Africa will also see its agricultural (79) decline. Coastal areas may also be affected by rising sea levels and intrusion of salt water into inland freshwater resources. The staple food for the region, maize, is particularly susceptible to drought. Wetlands of international importance and wildlife are also under threat from (80) in Southern Africa. Climate change, therefore, is expected to worsen the food supply, (81) , exacerbate the widespread poverty in the region.
Directions: There are 20 blanks in the following passage. For each blank there are four choices marked A, B, C and D. You should choose the ONE that best fits into the passage. Then mark the corresponding letter on the Answer Sheet. For the people who have never traveled across the Atlantic the voyage is a fantasy. But for the people who cross it frequently one crossing of the Atlantic is very much like another, and they do not make the voyage for the (41) of its interest. Most of us are quite happy when we feel (42) to go to bed and pleased when the journey (43) . On the first night this time I felt especially lazy and went to bed (44) earlier than usual. When I (45) my cabin, I was surprised (46) that I was to have a companion during my trip, which made me feel a little unhappy. I had expected (47) but there was a suitcase (48) mine in the opposite comer. I wondered who he could be and what he would be like. Soon afterwards he came in, He was the sort of man you might meet (49) , except that he was wearing (50) good clothes that I made up my mind that we would not (51) whoever he was and did not say (52) . As I had expected, he ’did not talk to me either but went to bed immediately. I suppose I slept for several hours because when I woke up it was already the middle of the night. I felt cold but covered (53) , as well as I could and tries to go back to sleep. Then I realized that a (54) was coming from the window opposite. I thought perhaps I had forgotten (55) the door, so I got up (56) the door but found it already locked from the inside. The cold air was coming from the window opposite, I crossed the room and (57) the moon shone through it on to the other bed (58) . there. It took me a minute or two to (59) the door myself. I realized that my companion (60) through the window into the sea.
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