This is an unpleasant subject __________ we might argue for a long while.

A．in which　

B．with them

C．about which　

D．with it

已知工作辊直径为650mm，压下量为20mm，轧辊与带钢的摩擦系数为0.23，，在没有外力作用下，请计算带钢能否被有效咬入？