Task: Question Generation
Input (English): Background Paragraph: Hydrogen bonds cause water to have a relatively high boiling point of 100°C (212°F). Because of its high boiling point, most water on Earth is in a liquid state rather than in a gaseous state. Water in its liquid state is needed by all living things. Hydrogen bonds also cause water to expand when it freezes. This, in turn, causes ice to have a lower density (mass/volume) than liquid water. The lower density of ice means that it floats on water. For example, in cold climates, ice floats on top of the water in lakes. This allows lake animals such as fish to survive the winter by staying in the water under the ice. 
Story: Bill was studying the states of matter. First, he selected a matter with low boiling point. He labeled it as matter A. To compare it with a well-known matter he selected water. He labeled it as matter B. He also selected ice, which he labeled as matter C. He is now better prepared to compare their states.
Output (English): Which would have lower density, matter B or matter C?