Task: Question Generation
Input (English): Background Paragraph: Blue ice occurs when snow falls on a glacier, is compressed, and becomes part of the glacier. Air bubbles are squeezed out and ice crystals enlarge, making the ice appear blue.

Small amounts of regular ice appear to be white because of air bubbles inside them and also because small quantities of water appear to be colourless. In glaciers, the pressure causes the air bubbles to be squeezed out, increasing the density of the created ice. Large quantities of water appear to be blue, as it absorbs other colours more efficiently than blue. A large piece of compressed ice, or a glacier, similarly appears blue. 
Story: Mike likes to visit places. This winter he is visiting Greenland. First, he visited Lake A, which is very small. Then he visited Lake B, which is huge. While visiting Lake B he went to a local pub. There he heard other tourists talking about two nearby glaciers, glacier C and glacier D. They said that glacier C had a snowfall and the snow became part of the glacier, but glacier D didn't have any snowfall. Mike is getting ready to visit those glaciers.
Output (English): Is ice thinner or denser in glacier D than in glacier C?