问题补充:
The old lady didn’t know when the house caught fire.
A. how to do
B. how to do with it
C. what to do
D. what to do it
答案:
A. how to do
B. how to do with it
(答案→)C. what to do
D. what to do it
解析:考查疑问词+不定式作宾语。此题中what+to do形成固定短语做know的宾语。句意:当她的房子着火的时候这位老妇人不知道做什么。所以选C。