Bythetimehewastwelveyearsold,he 

問題詳情：

 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

知識點：動詞時態與語態

題型：選擇題