When I last saw them, the police had chased the robbers down Columbus Street.

A．were chasing

B．was chasing

C．chased

D．were on a chase

只需摄仰卧腹部正位的疾病是（）

A.游走肾

B.肠梗阻

C.泌尿系结石

D.急性胃肠道穿孔

E.先天性肛门闭锁