题目

有关商品谷物农业的叙述，正确的是  (     )                                    A．商品谷物农业是一种购买农产品的农业地域类型 B．种植的作物主要是水稻和小麦 C．生产规模大，机械化程度高是商品谷物农业的基本特征 Ｄ．澳大利亚是世界上最大的商品谷物农业生产国 答案：CIf you ________ hard at high school, you ________ a college student now．A.had studied; would beB.study; should have beenC.had studied; will beD.study; must be