Consider the following university database schema:

Student (SID, Name, Age, Major, GPA)

Course (CID, Title, Department, Credits)

Enrollment (SID, CID, Semester, Grade)

Professor (PID, Name, Department, Salary)

Teaches (PID, CID, Semester)

Which of the following relational algebra expression(s) will  Find courses that are either taught by Professor A or taken by Student X but not both?  (Note: there can be more than expressions)