CREATE TABLE enroll (stu_num VARCHAR)
CREATE TABLE student (stu_num VARCHAR)

What is the first name of students who got grade C in any class?
SELECT DISTINCT stu_fname FROM student AS T1 JOIN enroll AS T2 ON T1.stu_num = T2.stu_num WHERE enroll_grade = 'C'
SELECT DISTINCT "stu_fname" FROM "student" AS "T1" JOIN "enroll" AS "T2" ON "T1"."stu_num" = "T2"."stu_num" WHERE "enroll_grade" = 'C'