Consider the TUTOR, TUTOR_ASSIGNMENT and COURSE relations that appear below. Show the results and the relational algebra expressions for the following four retrieval requests.
a. What are the Course IDs for those courses that do not have an assigned tutor?
b. What are the names of the tutors for MIS 4372?
c. What are the names of the tutors for those courses with no prerequisites?
d. What are the course names and number of prerequisites for those tutors hired in 2009?