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单项选择题

哺乳动物的精子在受精前要发生一个重要的变化，这个变化叫

A．、 皮层反应
B．、 透明带反应
C．、 精子获能
D．、 顶体反应
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未知题型
Even geologist is familiar with the erosion cyclE.No sooner has an area of land been raised above sea-level than it becomes subject to the erosive forces of naturE.The rain beats down on the ground and washed 1 the finer particles, sweeping them into rivulets and them into rivers and out to seA.The frost freezes the rain water in cracks of the rocks and breaks 2 even the hardest of the constituents of the earth's crust. Blocks of rock dislodged at high levels are brought down by the force of gravity. Alternate heating and 3 of bare rock surfaces causes their disintegration. In the dry regions of the world the wind is a powerful force in removing material from one area to another. All this is natural. But nature has also provided certain defensive forces. Bare rock surfaces are in 4 course protected by soil,itself de-pendent initially on the weathering of the rocks. Slowly 5 surely,different types of soil with differing 'profiles'evolve the main types depending primarily on the climatE.The protective soil covering,once it is formed,is hold together by the growth of vegetation. Grass and herbaceous plants, 6 long,branching tenuous roots,hold firmly together the surface particles. The 7 is true with the forest cover. The heavi-est tropical downpours beating on the leaves of the giant trees reach the ground only 8 spray,gently watering the surface layers and penetrating along the long passages provided by the roots to the lower levels of the soil. The soil,thus protected by grass,herb,or trees,furnishes a quiet habitat for a myriad varied organisms—earth-worms that importantly modify the soil,bacteria,active in their work of converting 9 leaves and decaying vegetation into humus and food for the growing plants. Chemical action is con-stantly taking 10 ;soil acids attack mineral particles and salts in solution move from one layer in the soil to another.
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未知题型
The number of people believing in religion (be) ______ increasing in Chin
多项选择题
以下做法，正确的有( )。
A.进他人办公室前应有规律的先敲三下门，征得同意后方可入内
B.下班后关闭电脑、打印机、空调等设备电源
C.拔打电话时，先询问对方是否方便接听电话
D.给同事起起绰号，无伤大雅
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