i don't know when to study and when to play.不是否定句么?怎么不用or?

i don't know when to study and when to play.不是否定句么?怎么不用or?

如果用or 的话,这句话应该是这么说的: i don't know when to study or play.
用and 在这里,其实完整的句子是 i don't know when to study and I don't know when to play. 我 不知道什么时候去学习也就不知道什么时候去玩了!
供你参考,希望能帮到你.

I don't know when to study and when to play.
说明：
用and表示对这两个事件都不知道，没有选择关系，所以不用or。
用or：
Which do you prefer,this one or that one?