--Have you finished your paper,John?--No,I ___my

问题描述:

--Have you finished your paper,John?--No,I ___my
--Have you finished your paper,John?
--No,I ___my mother in the kitchen all day yesterday.
A.had helped
B.had been helping
C.have been helping
D.have helped
求详解

B完成进行时为什么不选C是说昨天