Modal verbs

That restaurant [blank_start]must[blank_end] be very good. It's always full of people.

A: What are those people doing by the side of the road? B: I don't know. They [blank_start]might / may[blank_end] waiting for the bus.

Gary gave me a letter to post. I [blank_start]mustn't[blank_end] forget to post it because it is very important.

I am in a difficult position. What do you think I [blank_start]should[blank_end] do?

I am afraid I [blank_start]can't[blank_end] come to your party next week. I will be in London.