题目

_______ the letter , I ran out of the room to the post office. A Since I have finished writing                         B. No sooner than I had finished writing  C As soon as I finished writing                         D. After I have finished  答案：C探究物质性质二氧化碳是否可以溶于水，很难直接观察到现象，可以通过______的变化来间接感知．同样，研究氢氧化钠溶解于水时是吸热还是放热，就是利用______的变化引起了U形管内水位的变化，使______（填a或b）处的水位升高的．