Must be, might be, can't be, must have been, might have been, can't have been, should have been

I think they must be friends, because they are leaning against the same wall and they are about the same age.

They must be in spring or summer, because they are wearing short sleeve, dress and some one like these.

They might be playing games in their phones, because everybody are looking and typing their phones.

They might be waiting for another friend who gets late, because everybody are looking their phone. They should have met with him some time before.

They might be go out together for doing something, because they staying together waiting for someone.

The girl on the left might have dressed up, because the another girl is wearing a dress.