When you use "select ... into", make sure that the result of the query contains at most one row.

5.6 (c)

A student may have repeated Calculus 1 multiple times.

5.6 (e)

The question says "... are offered by the same department", not "... are offered by the same department of the professor", which means, for example, a CS professor can teach Math courses as long as he or she teaches only Math courses.

BTW, grading HW4 took longer than I expected, so the midterm grades probably won't be out until some time tomorrow.