Why does the blood returning to the heart have very little oxygen in it?

a)the heart is not pumping oxygen fast enough
b)the cells throughout the body used the oxygen.
c)the heart did not receive enough oxygen from the lungs
d)the lungs breathed out too much oxygen

Ineed an essay 1200words about obezity ,introduction, main causes, conclusion

Which criteria should andreas use when evaluating which monitor to purchase? check all that apply1. cost of monitor2. quality of monitor 3. doctor's recommendation4. whether it meets his requirements5. advertiser's claims

Oprincipal hormônio sexual masculino é a testosterona, que é produzida pelas células do testículo chamadas de células de leydig. o responsável por estimular a produção da testosterona é: escolha uma: a. o hormônio luteinizante. b. a progesterona. c. o hormônio folículo-estimulante. d. a androstenediona. e. o estrógeno.