— I telephoned him twice and I couldn't get through to him.

— I think that the line might have been out of  order, ____     ?   [ ]

A. don't you        

B. wasn't it    

C. do you    

D. hadn't it

下图是DNA分子复制的图解，请据图回答：

图中［2］过程表示以母链为模板进行的碱基的（），参与配对的物质是游离在周围的（）。