Task: Question Generation
Input (English): Background Paragraph: Liquid water is a fluid. The hydrogen bonds in liquid water constantly break and reform as the water molecules tumble past one another. As water cools, its molecular motion slows and the molecules move gradually closer to one another. The density of any liquid increases as its temperature decreases. For most liquids, this continues as the liquid freezes and the solid state is denser than the liquid state. However, water behaves differently. It actually reaches its highest density at about 4°C. 
Story: Mark decides he want a cold drink and puts a bottle of warm water in his freezer. By doing this he makes the water colder and as water cools its density increases eventually freezing and becoming a solid, Ice. After a while mark forgets that he put the bottle of water in the freezer. He eventually remembers and comes back to check and the bottle of water is frozen solid. Because of this he leaves the bottle out on his kitchen counter for a few hours and returns to a nice cold bottle of water.
Output (English): Which is denser, warm water or ice?