宏观截面是指中子与单位体积的所有（）或分子发生作用的截面。
A.质子
B.中子
C.电子
D.原子
参考答案：D
用所给词的适当形式填空
1. The story has a happy _ (end).
2. The reason why he came is not very _(convince).
3. Have you ever _ _(be) to the Water Park?
4. There was something wrong with my car yesterday, but a kind man gave me a _(rode).
5. My father ________ (work) in this factory since 1980.
交流接触器CJl2—250表示主触点额定电流为（）。
A、100A
B、150A
C、250A
D、300A
