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

c$)$ 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.

d$)$ Get the names of the instructors who are teaching at least two different courses in the same semester of the same year.

e$)$ Get the names of the courses that have two or more sections.