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: Scientists are finding more and more evidences of water in the outer space. Earth has mostly liquid water. But that's not the case with other celestial objects. Venus has some water, but it is in gaseous state. On the other hand, water in Jupiter's moon Europa is in frozen state.
Output (English): In which place the state of water is in lower density, Earth or Europa?