_______ 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

答案及解析： B

解析：

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。