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

When do people generally experience rapid growth for a second time? a. between the ages of 3 and 9 b. between the ages of 9 and 12 c. between the ages of 13 and 20 d. between the ages of 25 and 29 which action occurs in the third stage of cell division? a. the nuclear material of cell is copied exactly. b. the nuclear membrane disappears. c. the cell forms two nuclei d. the nuclear material separates, with half moving to either side of the cell.