___many times,but he made the same mistakes again.

题目

___many times,but he made the same mistakes again.
A.Having been warned B.Although I had warned him
C.Having warned him D.I had warned him
这题选D,说是but为并列连词,因此前一部分既非状语从句也非谓语动词形式.所以排除其他项
A B C 选项哪个是状语从句 哪个是非谓语动词形式啊?

答案

应选D
A中,应把but去掉
B中,although不能和but连用
C中,应用被动语态
AC为非谓语动词形式,B为状语从句