问题
选择题
| I'm very happy because it's my ______ fifteenth birthday today. |
A. a B. an C. the D. 不填 |
答案
答案：D
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| I'm very happy because it's my ______ fifteenth birthday today. |
A. a B. an C. the D. 不填 |
答案：D
。求：（1）这一过程中重力对物体所做的功。（2）这一过程中拉力对物体所做的功。（3）物体在A点具有的动能。