What is the circulatory system's function? : )
a. it removes cellular waste from the blood and converts it to urine.
b. it exchanges carbon dioxide and oxygen in the lungs.
c. it transports oxygen and nutrients to cells while removing carbon dioxide and other wastes
d. it breaks down food into usable parts.

What are four key elements of the study of economics?

Animal bodies (and even plant bodies for that matter) are complex enough that life couldn't exist without enzymes. enzymes are usually large, complex biological catalysts that are expensive to make. enzymes speed up the rate of chemical reactions without being used up during the reaction (they can be reused many times). they are highly specific in the reactions they regulate. knowing what enzymes are and how they function, why does this explain why complex life forms could not exist if there were no enzymes.

The wings of insects, birds, and bats evolved independently but carry out similar functions. this is an example of a. analogous structures. b. embryonic structures. c. vestigial structures. d. homologous structures.