Which are characteristics of mammals? check all that apply.

a) internal fertilization
b) three-chambered heart
c) endothermic
d) highly developed nervous system
e) several nearly hollow bones
f) always live on land

D, A, C

Explanation: I know this because Mammals sexually reproduce. The male sperm fertilizes the females egg. AKA internal fertilization. Endothermic is when an organism requires heat to survive. Yes, mammals need heat to live. that is why we are warm blooded. Mammals have a very complex nervous system otherwise we would not be able to feel anything.

answer: - b cells

explanation: -

so, the b cells mediate their action by identifying the antigens present on the surface of the pathogens and then producing antibodies in return to mediate its effect.

the answer is d. chordata