为自己加油

假设在 mysql 数据库中,有学生,成绩,老师,课程四张表,表结构如下 学生表,student ( s_id ,s_name ,s_age ,s_sex )教师表,teacher (t_id ,t_name )课程表,course (c_id ,c_name ,t_id)成绩表,score ( sc_id ,s_id ,c_id ,score )以下 sql 正确的是( ) 。

A.SELECT   student.s_id   ,  s_name   FROM   student   LEFT   JOIN   score   wherescorE.score>60
B.DELETE FROM teacher WHERE t_name LIKE '陈%'
C.ALTER TABLE teacher ADD COLUMN s_phone VARCHAR  ( 15 ) NOT NULL DEAFULT '' COMMENT '联系电话';
D.ALTER TABLE teacher ADD INDEX sid_index ON s_id;