Hydrogen bonds make water molecules spread out when they freeze. This makes ice less dense than water and allows ice to float. If ice did not float then oceans and lakes would freeze from the bottom up, killing marine life by trapping organisms in the ice. When ice floats, it insulates the water below, keeping it at around 4 degrees C or 40F, which does not freeze and allows fish to survive the winter.
Blood flow is greater when you exercise because the blood vessels in your muscles dilate. Imagine water flowing through a fire hose compared to a garden hose.
I believe the answer is A.), chemical compounds. It is definitively not B or C. Chemosynthesis produces energy by the oxidization of chemical compounds.