Mary has two brothers are doctors. A. both of theyB. both of whomC. both of themD. whom

问题补充：

Mary has two brothers, are doctors.

A. both of they

B. both of whom

C. both of them

D. whom of both

答案：

A. both of they

(答案→)B. both of whom

C. both of them

D. whom of both

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