题目

240. It is an important problem. You should ________ before you draw a conclusion. A. think about             B. think it over             C. think of it               D. think over it 答案：B下列说法中正确的是  （     ）A. 用铁与稀硝酸反应来制备氢气      B. SO2能使湿润的蓝色石蕊试纸先变红后退色C．NO2 溶于水发生了氧化还原反应，它既是氧化剂又是还原剂D．钠在氧气中燃烧发出白光，生成白色固体氧化钠