1.You can leave town at once.
3.You might at least leave town at once.
5.Shall I leave town at once?
7.You canít leave town at once.
8.Can he have left town at once?
9.He canít have left town at once.
Vil - there is a fatal flaw in this exercise: 'wording' is one thing, but when would a native speaker say/ask some of these? And would we use ''at once', or 'straightaway'?
Just from the few above, can you give me a scenario where someone would say,"8.Can he have left town at once?" or No.9?