Although ________ after the Civil War, the American blacks still took no important role in the white Americans except as servants and laborers.

A．no longer being slaves

B．were no longer slaves

C．no longer slaves

D．no longer been slaves

全部半贫液泵均不上量的处理方法是（）

A、脱碳系统作停工处理

B、停止两塔循环

C、降低贫液量

D、降低装置处理量，提高贫液量