A:going o
B:goes o
C:went o
D:to go o
选择方框内合适的短语并用其正确形式填空。
be used to take possession of be likely to
set off in the style of be devoted to go through
如图所示,一个质量为m的小球用长为l的轻绳悬挂于O点,小球在水平拉恒力F的作用下,从平衡位置P点很缓慢地移动到Q点,则水平力F所做的功为( )