One day while I ____ along the street,I ____ someone calling.

问题描述:

One day while I ____ along the street,I ____ someone calling.
A.walked…was hearing B.was walking…has heard
C.was walking…had heard D.was walking…heard
为什么选D不选C

因为had heard是过去完成时,表示“过去的过去”发生的行为
本题没有这个意思,就是指“在过去某个时间点听到”,所以用一般过去时.