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
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A. Do you think which of these
(答案→)B. Which of these do you think
C. Which of these you think
D. You think which of these
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。