由蛇形管组成的省煤器，安装完毕后应( )。

A．检查肋片的损坏数量

B．检查联箱内部情况

C．清理杂物

D．进行通球试验

Since______beginning of photography,______inventors have tried to make______ photographs that duplicate______natural colors.

A．the.../.../.../


B．the...the.../...the
C．/.../.../.../


D．/...the...the.../