Which of these is the human body's first line of defense against invading pathogens such as bacteria and viruses?

Long-period comets come from the oort cloud particles in earth’s atmosphere material from the asteroid belt the kuiper belt

Immature bone cells, or osteoblasts, manufacture a protein called osteoid as well as several hormones. because of this, we would expect osteoblasts to contain numerous a) nuclei. b) ribosomes. c) lysosomes. d) golgi bodies.

Which structure in the cardiovascular system connect arteries to veins?