It was ______ back home after the experiment. 

A． not until midnight did he go

B． until midnight that he didn’t go

C． not until midnight that he went

D． until midnight when he didn’t go

引起输尿管梗阻的最常见原因是（）

A.结核

B.结石

C.炎症

D.输尿管囊肿

E.肿瘤