[2] Please draw an ERD based on following description. a) In a school, each department has many professors assigned to it. A professor belongs to one department. Among professors, some chair a department. A department must have only one chair. And no professor is required to accept the chair position. Therefore, DEPARTMENT (which has attribute: Name) is optional to PROFESSOR (which has attributes: ID. Name, hired-year, rank) in the "chairs relationship. [3] Please draw an ERD based on following description. a) Each professor (attributes: ID, Name, rank) may teach up to four classes. b) Each class is a section (attribute: Section ID of a course (course ID, title). c) A professor may also be on a research contract and teaches no classes at all. d) Each class is taught by a professor