Have you ever met with this case in your life 　　　　 you can't understand others

even if they have said something several times？

A．where

B．what

C．that

D．which

非水平燃气、热力管道的绝热施工应（）进行，防潮层和保护层的搭接应（）。

A、自下而上；下压上

B、自上而下；下压上

C、自上而下；上压下

D、自下而上；上压下