To finish the task, we’re tried three times, and after dinner we’ll try _____ time. A. the fourth B. a fourth C. fourth D. four 答案:B有机物A和B,只由C、H、O两种或三种元素组成,相同物质的量的A和B完全燃烧时,消耗氧气的物质的量相等,下列对A、B的判断错误的是 A.A与B互为同系物 B.A与B的分子组成相差n个“CH2” C.A与B的分子组成可能相差n个“CO2” D.A与B的分子组成可能相差n个“H2O”