【单选题】
删除计算机系学生（在student表中）的修课记录（在SC表中）的语句，正确的是（ ）。
①
DELETE FROM SC JOIN Student b ON S.Sno = b.Sno WHERE Sdept = 计算机系
②
DELETE FROM SC FROM SC JOIN Student b ON SC.Sno = b.Sno WHERE Sdept = 计算机系
③
DELETE FROM Student WHERE Sdept = 计算机系
④
DELETE FROM SC WHERE Sdept = 计算机系