They day _____I became a Young Pioneer was the happiest day in my life.

题目

They day _____I became a Young Pioneer was the happiest day in my life.
A that B where C when D which

答案

The day _____I became a Young Pioneer was the happiest day in my life.
C when
选择WHEN,我成为少先队员那天是我一生中最开心的一天.
那天是时间,所以用WHEN.