题干
Look! It is _______ CD. It's ________ CD.
A：a; his
B：his; an
C：a; I
D：an; her
答案(点此获取答案解析）
A
Look! It is _______ CD. It's ________ CD.
A：a; his
B：his; an
C：a; I
D：an; her
的前
项和
，
，公差
，则
=
