题干
Mr. Chen has ______ useful horse and ______ horse can do a lot of things for him.
A：a; a
B：an; a
C：a; the
D：an; the
答案(点此获取答案解析）
C
Mr. Chen has ______ useful horse and ______ horse can do a lot of things for him.
A：a; a
B：an; a
C：a; the
D：an; the
（
是常数）表示的平面区域面积是9，那么实数