—I counted sheep, I drank milk and I tried everything, but nothing helped.

—It seems you _____ too much recently. Try some sleeping pills.

A．worked

B．work

C．had worked

D．have been working

如图，悬线AO与天花板夹角为60°，线BO水平，所挂物体的重力为G．求悬线AO和BO的拉力大小．