BE SUPPOSED TO
Mike is supposed to call me tomorrow.
(IDEA: I expect Mike to call me tomorrow.)
We ate supposed to write a composition.
(IDEA: The teacher expects us to write a composition).
It is supposed to rain today.
(IDEA: People expect it to rain today.)
Alice was supposed to be home at ten.
(IDEA: Someone expected Alice to be home at ten.)
Be supposed to is used to talk about an activity or event that is expected to occur.
In (a): The idea of is supposed to is that Mike is expected (by me) to call. I asked him to call me. He promised to call me. I expect him to call me.
NOTE: The present form of be is used for both future expectations and present expectations
