Find names of all students who took some course and got A or C.
SELECT T1.stu_fname ,  T1.stu_lname FROM student AS T1 JOIN enroll AS T2 ON T1.stu_num  =  T2.stu_num WHERE T2.enroll_grade  =  'C' OR T2.enroll_grade  =  'A'
students who got A or C in some course refers to WHERE enroll_grade = 'A' OR enroll_grade = 'C'; names refer to SELECTing the first name (stu_fname) and last name (stu_lname);