现有学生表student_tb,其字段有:name(学生姓名),classid(班级编号),sex(学生性别),统计 student_tb 表中男生人数的SQL是()。
A、select count(*) from student_tb where sex = '男';
B、select sum(*) from student_tb where sex = '男';
C、select avg(*) from student_tb where sex = '男';
D、select max(*) from student_tb where sex = '男';