Question

they write letters to each other very often

Betty has a pen pal．They often write letters to each other _______English．（　　）

A. by

B. on

C. of

D. in

Answer 1

答案：D．
结合语境可以推断这句话表达的意思是"Betty有一个笔友，他们经常用英语给彼此写信．"，所以设空处的介词短语表达的意思是"用英语"，应该用介词in，故选D