A stands out most to me, CO comes from the air and air is basically oxygen we breath. When we exhale CO comes out (of course). I would say A is correct.
Things of the same species have similar morphology and can INTERBREED
<span>Epithelial and connective tissues combine to form four types of membranes: mucous membranes (epithelial tissues are moist), serous membranes (line cavities that are not open to the outside environment), cutaneous membranes (skin that covers the surface of the body), and synovial membranes (produce synovial fluid).</span>
