问题补充：
-----What’s your plan for your winter holiday ?
----- I haven’t decided .
A. where to do it
B. how to do
C. what to do it
D. what to do
答案：
A. where to do it
B. how to do
C. what to do it
(答案→)D. what to do
解析：本题主要考虑的是特殊疑问词+动词不定式短语，如果是特殊疑问词是疑问副词后接to +不及物动词，或特殊疑问词（疑问副词）+to 及物动词+宾语；或疑问代词+to +及物动词或疑问代词+to +不及物动词+介词，本题符合疑问代词+to +及物动词，故选D
