A:where
B:which
C:how
D:why
如图是重0.6N的小球从水平桌面下滚下时的频闪照片.请画出小球在A位置时所受重力的示意图.
—Hey, turn it off, please! We don't music in the reading room. ——Oh, I'm sorry, sir. I won't do it again.