the old lady used to_under a big tree,waiting for her _ son to come back
问题描述：
the old lady used to_under a big tree,waiting for her _ son to come back
A:sit;missing
B;sitting:missed
C;sit:missed
D;sitting:missing
答
A
used to do 过去常常
be used to doing 习惯做……
be used to do 被用来做
a missing boy 一个失踪的男孩