when did he leave?when did he leave?这里为什么不用leaves而用leave呢,

when did he leave?when did he leave?这里为什么不用leaves而用leave呢,
when did he leave?
when did he leave?
这里为什么不用leaves而用leave呢,

when did he leave?when did he leave?这里为什么不用leaves而用leave呢,
前面有助动词did 了,如果前面有does ,后面也用动词原形.

did后面需要动词原形。且leaves是一般现在时而did是一般过去时，不可能在此句中同时出现。