He has finished his homework when his mom went home.那为什么说when 不可以和现在完成时用？

He has finished his homework when his mom went home.那为什么说when 不可以和现在完成时用？
He has finished his homework when his mom went home.
那为什么说when 不可以和现在完成时用？

He has finished his homework when his mom went home.那为什么说when 不可以和现在完成时用？
是的,把has 改成had.发生在过去的过去的动作要用过去完成时

当他妈妈到家的时候他已经做完作业了
had

把has改成had ,因为从句部分已经是过去式了，主句要用过去完成时