We can't...
We must...
They must have...
We should have...
They could have...
They might...
You don't have to...
...played for a bit longer, but they didn't.
...take drinks into the concert. It's not allowed.
...forgotten about meeting us here.
...play my favourite song. I hope so.
...shout! We can hear you!
...remember the tickets.
...bought tickets closer to the front. It's hard to see.