--Did you listen to the report last Friday?

--- Yes, it was about the shortage of migrant workers. That was the first time I______ about the subject.

A．heard

B．was hearing

C．would hear

D．had heard

脑栓塞的栓子来源最常见的是（）

A.心源性栓子

B.感染性脓性栓子

C.脂肪栓子

D.癌性栓子

E.气体栓子