—  ______ that he picked up his uncle at the airport? 

—  It was at 6:00 in the afternoon ______ he got off work.  [ ]

A.  Was it when; that    

B.  When was it; that    

C.  Was it when ; when    

D.  When was it; when

配电线路导线连接管必须采用（）的材料制成。