When you are learning a foreign language you must forget your own language.A. at the f

问题补充：

When you are learning a foreign language, , you must forget your own language.

A. at the first

B. first of all

C. in first

D. first at all

答案：

A. at the first

(答案→)B. first of all

C. in first

D. first at all

解析：本题的含义是当你学习一门外语的时候，首先你必须要忘记你自己的语言，first of all表示首先的意思，故本题选B。