旋风分离器的主体上部为圆筒，下部为一圆锥形底，锥底下部有排灰口，圆筒上部装有顶盖，侧面装一（），圆筒的上部中央处装一排气管。

A、圆形截面进气管

B、正方形截面进气管

C、矩形截面进气管

D、梯形截面进气管

She was educated at Beijing University, __________ she went on to have her advanced study abroad.

A．after which

B．from which

C．from that

D．after that