--
--She is tired and hungry.
A:What's her name?
B:How is Kitty?
C:What can she do?
西汉初年,皇帝找不到颜色相同的四匹马来驾车,将相大臣甚至只能乘坐牛车;到汉武帝初,普通百姓也拥有马匹,“阡陌之间成群”。马匹大量增加的主要原因是( )