When or if: Choosing the Right Word
先写下记得的内容，再查看解释。不要填写个人信息。
查看解释
When introduces a time and often presents an event as expected. If introduces a condition. That condition may be uncertain, or it may describe a repeated situation. The choice tells us how the speaker presents the event; it does not guarantee what will happen.
When our manager arrives at nine, we will start the project presentation.