题目

The meat is ________．A. fifteen yuan a kilo B. fifteen yuans a kiloC. fifteen yuan kilos D. fifteen yuans kilos 答案：【答案】A【解析】句意：这肉每公斤十五元。考查名词的数。货币单位“yuan”是不可数名词，“每公斤十五元”是fifteen yuan a kilo；故选A。（2002•咸宁）边长为a的正n边形的内角和是720°，则此正n边形外接圆的半径长等于    ．