Given the following relational database schema:

Student = (SSN, Name, Major)

Course = ( CourseNumber , CourseTitle, NumberOfUnits, RoomNumber, DayTime), where DayTime is of the form MW 1:0-2:00.

Enrollment = (SSN , CourseNumber, Grade)

Use SQL to express the following queries using a minimal number of tables and operations.

a: List the SSN and the name of every student who does not have a grade in any course, i.e all her or his grades are null.

b: List the name of every student who hasnt taken any course.