It is often said that        teachers have         very easy life.

A．the; a

B．/; a

C．the; /

D．/；the

典型的后方回声增强不常见于以下哪项含液性结构（）

A.囊肿

B.新鲜血肿

C.囊状扩张的肝内胆管

D.扩张的肾盂和输尿管

E.胸膜腔积液