"The tea is good. _____, please?"

"Certainly. I'm very glad you love it." [ ]

A. Could I have another cup

B. Why not have a cup

C. Where did you buy it

设有关系模式SC(sno，cno，grade)，查询既选修了c1又选修了c2课程的学生学号，正确的SQL命令是

A．SELECT sno FROM sc WHERE cno="c1"AND cno="c2"

B．SELECT sno FROM sc WHERE cno="c1"AND SELECT sno FROM sc WHERE cno="c2"

C．SELECT sno FROM sc WHERE cno="c1"UNION SELECT sno FROM sc WHERE cno="c2"

D．SELECT sno FROM sc WHERE cno="c1"AND sno IN(SELECT sno FROM sc WHERE cno="c2")