一个多边形的每一个外角都相等，一个内角和一个外角之比为9：2，求这个多边形的边数．

选出所给句子的答句，将其字母代号填在括号内。

①Is this your jacket?____                     A. I'm ill.

②What's the time?____                       B. All right.

③Shall we copy it now?____                   C. No, it isn't.

④What's the matter?____                      D. Four thirty

⑤My pencil is too short.____            E. You can have this long one.

下列句子表意明确、没有语病的一项是（）