能保证准确瞬时传动比的机械传动有（）。
A.螺旋传动
B.带传动
C.链传动
D.齿轮传动
E.蜗杆传动
参考答案：D, E
在图中用笔画线代替导线，把灯L1、L2组成并联电路，要求开关S能同时控制灯
L1和灯L2，用电流表测通过L2的电流．并画出对应电路图。
用括号内所给单词的适当形式填空。
1. Our library needs 45 Chinese-English____ (dictionary).
2. The boy enjoys____(play) chess with his grandfather.
3. His sister is a nurse now, but she wants (be)a reporter.
4. These sports____ (activity) are for students.
5.--What's the weather like in your city?
-- It is (sun)．
