— What’s the matter with you?

—______the heavy suitcase, my waist was hurt unexpectedly.

A．Carrying

B．Carried

C．While carrying

D．While I was carrying

直流电机中的换向器是由（）而成。

A、相互绝缘的特殊形状的梯形硅钢片组装

B、相互绝缘的特殊形状的梯形铜片组装

C、特殊形状的梯形铸铁加工

D、特殊形状的梯形整块钢板加工