构成结核病重要传染源的肺结核类型是（）

A.陈旧生肺结核

B.急性粟粒型肺结核

C.血行播散型肺结核

D.浸润型肺结核

E.慢性纤维空洞型肺结核

It is human nature to think back to a golden age _____ one's country was strong and respected. [ ]

A. if

B. when

C. while

D. after