Mr Philip has made ______ survey on students’ lunchtime, and ______ survey shows us a lot of problems.

A．an; an

B．the; the

C．a; the

D．the; a

传染病患者排出病原体的整个时期称为（）

A.传染期

B.感染期

C.感染前期

D.潜伏期

E.检疫期