Answer:
Shape of Red Blood Cells Erythrocytes are biconcave discs with very shallow centers. This shape optimizes the ratio of surface area to volume, facilitating gas exchange. It also enables them to fold up as they move through narrow blood vessels.
Population and nutrients, This is because if you have a large population then you must need a certain amount of nutrients to suit the population
Answer: E. Polygenic
Explanation: The color of eyes and hair is due to quantity and accumulation of pigments such melanin. Melanin is synthesize by multiple enzymatic steps and every enzyme is codified by a different gene. That means polygenic inheritance, that several genes are implicated in determined the this trait and its difficult to trace since every gene has a sequence that can vary between families or human groups.
Because they are made mostly or partly out of gas.