I went to the office then I remembered it was my day off. HAVE I ..... to the office as it was my day off.
need not have gone, needn't have gone
Perhaps we missed the correct turning. MIGHT We ..... the correct turning.
might have missed, might've missed
I'm afraid you can't smoke in here. ALLOWED You ..... in here.
are not allowed to smoke, 're not allowed to smoke, aren't allowed to smoke