力矩的正负号规定是：（）为正；反之为负。

A．力使物体绕矩心逆时针转动

B．力使物体沿坐标轴正向运动

C．力使物体绕矩心顺时针转动

D．力使物体沿坐标轴负向运动

— The problem is a bit difficult .

— ________ask your teacher for help?

A．Why not

B．What about

C．Try to

D．You should