--I want to know when Mr. Brown will arrive.--When he I will tell you. A. will arrive B.

问题补充：

--I want to know when Mr. Brown will arrive.

--When he , I will tell you.

A. will arrive B. arrived C. arrives

答案：

解析：考查状语从句的用法。用when引导的时间状语从句，用一般现在时表示将来；“主将从现”，主语是单三，动词用单三形式arrives。