4) Let p and q be the propositions "You are a freshman," and "You are enrolled in three courses for this semester, "respectively. Express the following compound proposition as an English sentence [0.75pt]:Tqp a) You are notenrolled in three courses for this semester if and only if you are not a freshman b) You are not enrolled in three courses for this semester if and only if you are not a freshman c) You are enrolled in three courses for this semester if and only if you are a freshman (d) You are notenrolled in three courses for this semester if and only if you are a freshman