She decided to do ____ a lot of other girls were doing those day

She decided to do ____ a lot of other girls were doing those days.
A、how
B、why
C、which
D、what
【正确答案】：D
【题目解析】：do后面缺少宾语，what a lot of other girls were doing those days许多其他女孩子这些天正做的。