Hormones because if you think about it. Vertebrates must have backbones and mammals have them. And, humans are basically mammals. And the glands secrete hormones.
Answer:
A. It's a reliable source because it's from the government, not a website based on other people's opinions.
I have no idea what that means but the answer is b
DNA is the answer (if you could put me brainliest that would be great)
