问题补充：
I lost my friend’s bike, and I really don’t know .
A. what should I do
B. what to do
C. how shall I do
D. how to do
答案：
A. what should I do
(答案→)B. what to do
C. how shall I do
D. how to do
解析：I really don’t know后如果跟宾语从句，从句要用陈述语序，所以排除A,C；句中不定式to do后缺do的宾语，所以选B。
