a large crowd ___widly as the pilot ___her plane safely in california

问题描述:

a large crowd ___widly as the pilot ___her plane safely in california
a had cheered was landing
b had cheered landed
c was cheering had landed
d was cheering landed 这题选d我想知道为什么c是错的

这是关于as用法的题目.
as 引导的时间状语从句,“当...”的意思,与when等同.其主句用过去进行时,从句要用一般过去时.c was cheering;had landed错在 后半句时态不对.