he said he liked biology and wanted to be an animal doctor when he grew up

问题描述:

he said he liked biology and wanted to be an animal doctor when he grew up
为什么要用grew up 而不能用 grows ,不是现在还没长大吗

用when做时间状语连接副词时,主句和从句谓语动词时态要保持一致,前面wanted为一般过去式,所以grew用一般过去式