题干
-This is ____________ useful book, I think.
-So it is, and it's ____________ unusual one.
A：an; /
B：an; an
C：a; an
D：a, a
答案(点此获取答案解析）
C
-This is ____________ useful book, I think.
-So it is, and it's ____________ unusual one.
A：an; /
B：an; an
C：a; an
D：a, a
