There are ______ months in a year and December is ______ month.（ ）A. Twelve，twelfthB. twelfth，the twelfthC. Twelve，the twelfthD. twelfth，twelve

根据题干，可知考查数词的用法。twelve 基数词，十二，修饰复数可数名词；twelfth 第十二，序数词，常修饰单数可数名词。根据题干结构"There are ______ months in a year and December is _____ month."一年中有十二个月，十二月是第十二个月。可知，第一空用基数词，twelve；第二空用序数词，twelfth。序数词前通常要用定冠词the修饰。