如图所示，粗糙水平桌面上有一粗细均匀的导线制成的矩形线圈ABCD，其左侧外上方有一条形磁铁，磁铁不动时，线圈的AB边和CD边对桌面的压力均为N。当磁铁竖直向下运动到虚线位置的过程中（线圈始终不动）
A.AB边对桌面的压力大于N，CD边对桌面的压力小于N
B.AB边对桌面的压力小于N，CD边对桌面的压力大于N
C.AB边和CD边对桌面的压力都大于N
D.AB边和CD边对桌面的压力都小于N
答案：B
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| Most adults once studied at school, had classes and did homework every day. The same _1 is going on at school now. _2_it seems that doing weekend homework is 3_problem for the modern students. All the students should agree that weekend homework should be abolished (取消). It's 4 for them studying at school five days a week. They have a lot of interests. With homework to do on Saturday and Sunday, when can they find 5 to help around the house, go and see a football or basketball game or a good film, join in family recreations (娱乐), or just have 6 at home? Because of these other activities, the homework can not be finished until _7 . So their weekend homework is usually done in such a hurry that on Monday the 8 teachers often threaten (威胁) to fail whole class of students because they know nothing about the _9 . If there were no weekend homework for the students to do, they would be happy to school on Monday 10_having a good rest and to learn what the teachers teach. | ||||
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