Draw an ER diagram that shows the organization of a simple student database. The database captures the information about letter grades obtained by university students who enrolled in some sections of courses taught by some professors. In the database, each student is represented by a student ID and student name. Each course is represented by a course ID, a course name, and the number of credits assigned to the course; each section of a course is represented by a section ID (e.g., section "A01" of the 3-credit course "COMP 3380" named "Database concepts and usage").
Each professor is represented by the ID, name, office number and email address of the professor. Here, we assume that
(a) a student cannot repeat any courses,
(b) a student may take different sections of a course (e.g., COMP 4060 A03 and A08), and
(c) each course section is taught by one professor. Hint: Make sure you clearly identify the primary key of each entity set, the mapping cardinality of each relationship set, and also explicitly state the primary key of each relationship set.