题目

不能用来鉴别CO和CO2两种气体的方法是A．通入澄清石灰水              B．观察颜色C．通入紫色石蕊试液            D．点燃 答案：BMany of the students were busy ________ the party. [　　] A．preparing forB．to prepare C．prepareD．to prepare for