—My son is lost . Have you seen a boy passing by here?

—I saw        boy hidden behind          tree over there . You may go and have a look.

A．a; the

B．the; the

C．a; a

D．the; a

肠伤寒发病1周之内，取哪一种标本，细菌检出率最高（）

A.尿液

B.血液

C.唾液

D.胃液

E.粪便