Tom Mary speaks Chinese well so they can communicate with Chinese students very well.A.

问题补充：

Tom Mary speaks Chinese well, so they can communicate with Chinese students very well.

A. Neither ; nor

B. Not only ; but also

C. Both ; and

D. Either ; or

答案：

A. Neither ; nor

(答案→)B. Not only ; but also

C. Both ; and

D. Either ; or

解析：根据后半句的意思：因此谈们都能和中国学生很好的交流。可知汤姆和玛丽说汉语说得都非常好，可排除A和D,根据前半句的谓语动词speaks，可排除C，Not only ， but also连接两个主语时用就近原则，所以选B。