12. Mr Black has two sons are fond of collecting stamps.A. all of whomB. all of themC. b

问题补充：

12. Mr Black has two sons, are fond of collecting stamps.

A. all of whom

B. all of them

C. both of them

D. both of whom

答案：

A. all of whom

B. all of them

C. both of them

(答案→)D. both of whom

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