A:having bee
B:there being
C:having to be
D:there to be
一个滑轮起重装置如图所示,滑轮的半径是10cm,当重物上升10cm时, 滑轮的一条半径OA绕轴心O按逆时针方向旋转的角度约为(假设绳索与滑轮之间没有滑动,取3.14,结果精确到1°)( )
—That's right. You'd better take all umbrella with you.