$[33$ Marks$]$ Specify the following queries in relational algebra based on the database schema of Figure $2.$

b$)[7$ marks$]$ Select the students who $($a$)$ took all the courses, which the student whose ID is $1234567$ took, and $($b$)$

obtained in these courses the same grade as the grade of the student whose ID is $4567890$ in the Database

course that was offered in the Fall $2019$ semester.

c$)[7$ marks$]$ Get the names of the instructors who are teaching at least two different courses in the same semester

of the same year.

d$)[7$ marks$]$ Get the names of the courses that have two or more sections.