once引导什么从句,从句有时可省略

　　If I've said it once, I've said it a hundred times.

　　这事我曾经说过，而且是说过很多次了。

　　An opportunity like this comes once in a lifetime.

　　像这样的机会一生也许只会遇到一次。

　　It made a refreshing change to be taken seriously for once.

　　总算有一次受到认真对待，这变化真是令人耳目一新。

　　He was once the great white hope of British boxing.

　　他一度曾是英国拳击的希望所在。

　　We need to settle this once and for all.

　　我们需要把这事一次解决。