he was not sure _____for his mother's birthday.

问题描述:

he was not sure _____for his mother's birthday.
A waht was he going to buy B waht he was going to buy
C to buy what D waht he is going to buy
答案是B请问C错在哪里

带疑问词的不定式结构:
疑问词+ to do sth
what to buy 就对了