Given the following relational database schema:

Student = (SSN, Name, Major, TotalUnitCompleted)

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 has no grade in at least two of her/his courses.

b: List the name and SSN of every student who has completed the highest total number of units