If you schedule from the project start date and the calculated project finish date is before the expected project finish date, then

a$.$ the project cannot be finished before the expected project finish date if any of the tasks slip.

b$.$ the project does not have any slack before the expected project finish date.

c$.$ the project will always be finished under budget.

d$.$ the project has slack that is equal to the difference in time between the calculated finish time and the expected finish time.