Bythetimehewastwelveyearsold,he 

问题详情：

 By the time he was twelve years old ,he  ____ a chemistry lab of his own.   

A . had been set up         B.  had set up 

C. have been set up         D.  have set up

【回答】

B

知识点：动词时态与语态

题型：选择题