With ail the magazines I needed _________,I left the post office.                       

A．buying

B．to buy

C．bought

D．to be bought

人孔通常安装在（）。

A.切断装置后

B.补偿器、蝶阀后

C.沉积物易于聚集的特低管段

D.煤气管道的末端