Answer: C) Centromeres
Explanation: Centromeres are involved in crossing over, none of the other ones are.
gametangium is the problem
C: geographic distribution
<span>Gills enhance diffusion between aquatic creatures' blood and the surrounding water. They have a large surface area to increase the area available for gas exchange and a lot of capillaries to increase the bloodflow through the gills. The cells in the capillaries are flattened, which further increases their surface area and the rate of gas exchange.</span>