leave的过去式是leaved还是left?

leave的过去式是leaved还是left?
书的内容要求：
Present and Past Tense Verbs
A verb changes to show when an action happens.
Use a present tense verb to tell what happens.now.
leave The hardest part was when someone _____ to go war.
即：The hardest part was when someone leaved to go war.
（最难的部分是当一个人离开去战争）