When water in a lake freezes, the ice that forms floats on top of any water that is still liquid. Why does the ice float? A. Ice is less dense than liquid water, so it floats.
B. Air bubbles trapped in the ice cause the ice to float.
C. Ice crystals are polar, and they float on top of non-polar water.
D. The ice forms at the top of the water, so it stays there and floats.

A. Ice is less dense than liquid water, so it floats.

Explanation:

In fact, ice is around 9 percent less dense than water. As the water gets thicker, the lighter ice moves, allowing the ice to rise to the surface.

parasites can detrimentally affect their host, but also must not allow their host to die before they can complete their life cycle. some parasites have complex life cycles with many different hosts, and have had to find ways of persisting in many different environments during the change from one host to another. ectoparasites live outside the body of the host, and can more easily  disperse, but are  more exposed to predators, parasites, parasitoids. endoparasites live inside the body of the host, and are therefore protected from the outside environment. but they can be  attacked by the host's immune system. they have therefore developed  mechanisms for dispersal such as  complex life cycles.