问题
选择题
_______ is the most useful invention?
A．Do you think which of these
B．Which of these do you think
C．Which of these you think
D．You think which of these
答案
答案：B
考查插入语。do you think是插入语，去掉后不影响句意，当that后用特殊疑问词时，不能省略that，A项错。故选B。