Do you know A. what is this used for B. what this is used forC. which this is used D. tha

问题补充：

Do you know

A. what is this used for

B. what this is used for

C. which this is used

D. that this is used for

答案：

A. what is this used for

(答案→)B. what this is used for

C. which this is used

D. that this is used for

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