Mom often has conversations with my sister over ________ phone, while keep in touch with me by ________ letterMom often has conversations with my sister over ________ phone, while keep in touch with me by ________ letter.

A.不填; the

B.不填; a

C.the; 不填

D.the; a

答案及解析： C

解析：

第一个空填the是特指那部电话；

第二个空不填；

by letter固定搭配，用通信的方式第一个空填the是特指那部电话；

第二个空不填；

by letter固定搭配，用通信的方式。