Students (sid: integer, sname: string) Course (cid: integer, iid, cname: string) Instructors (iid: integer, iname: string) Grades (sid, cid, ggrade: string) The key fields are underlined, and the domain of each field is listed after the field name. Thus, sid is the key for Students, cid is the key for Courses, and iid is the key for Instructors. Based on the above schema, write the following queries in Relational Algebra and Domain Relational Calculus: 1. (8 Points) Find the snames of the students who registered in the course with cname "Database". 2. (8 Points) Find the snames of students who got a ggrade "A" in all courses. 3. (8 Points) Find the cids of courses taught by at least two different instructors. 4. (8 Points) Find the sids of students who never received a ggrade "D. 5. (8 Points) If grades are graded by 100 scale. Consider Scheme: Grades (sid, cid, ggrade: int) instead. Find the sids of students who received the highest grade