问题
选择题
| — _____? — I'm doing my homework. |
A. What does he do B. What do you do C. What are you doing |
答案
答案：C
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| — _____? — I'm doing my homework. |
A. What does he do B. What do you do C. What are you doing |
答案：C
的匀强电场中，有一带负电的物块A放在倾斜的木板上，物块所受电场力的大小为其重力大小的一半，木板的倾角α为
和
