Not only John and Tom but also their sister Mary great interest in the piano lessons.A.

问题补充：

Not only John and Tom but also their sister, Mary, great interest in the piano lessons.

A. take

B. takes

C. have taken

D. had taken

答案：

A. take

(答案→)B. takes

C. have taken

D. had taken

解析：考察主谓一致。Not only…but also…做主语时，谓语动词后后一个保持一致。故本题与their sister Mary保持一致，用单数形式，本题又是一般现在时，故B正确。