【正确答案】 C

【答案解析】 疑问词who，what，which，when，where和how后加不定式可构成一种特殊的不定式短语。它在句中可以用作主语、宾语、表语和双宾语等。①作主语：When to start has not been decided. (何时动身尚未决定。)②作宾语：I don't know what to do. (我不知道该怎么办。)③作表语：The difficulty was how to cross the river. (困难在于如何过河。)④作双宾语：I can tell you where to get this cake(我可以告诉你哪儿可以买到这种蛋糕。)本题考查该结构作宾语的情况。