问题描述：
1、（ ）Millie looks unhappy today.What _________ to her.
A、happened
B、did happen
C、has happened
D、was happened
2、Look,the rain __________(stop).Let us go.
第一题为什么不能选C
A、happened
B、did happen
C、has happened
D、was happened
2、Look,the rain __________(stop).Let us go.
第一题为什么不能选C
问题解答：
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