题目

________ preparations from now on，she would be able to finish the essay on Sunday.  A．Would she make      B．If she make  C．Were she to make     D．If she had made 答案： C 省略了if (If she were to make preparations from now on)，将were提前，表示与将来事实相反的虚拟条件句。                                             有机物X、Y分子式不同，它们只含C、H、O元素中的两种或三种，若将X、Y不论何种比例混合，只要其物质的量之和不变，完全燃烧时耗氧气量和生成水的物质的量也不变．X、Y可能是（　　）A．C2H4、C2H6OB．CH4、C2H4O2C．C2H6O、C3H6O2D．C2H2、C6H6