A.select*from student where course1+course2+course3>60
B.select*from student where course1 and course2 and course3>60
C.select*from student where max（course1，courser2，course3）>60
D.select*from student where course1>60 and course2>60 and course3>60

A.select count（）from student
B.select count（*）from student
C.select columns（）from student
D.select columns（*）from student