when跟once引导时间状语从句有何不同

when跟once引导时间状语从句有何不同

前者多表示时间，后者表示条件。
when asked whether i liked it, i nodded.

once you see her, you will never forget her

是时间状语从句，表示 一旦....就... 例如：he will not be swerved from his course once his mind 's made up. 一旦他已下定决心，就无法改变。