Answer:
the second option is correct.
Answer: the capillaries.
<span>The blood capillaries are blood vessels with very small caliber. They form the blood distribution and collection network in cells. They are the communication between branches
originating from the arteries and with the smaller
veins. It is on the walls of the capillaries that occurs <span>the exchange of water, oxygen, CO2,
other nutrients and chemical residues.</span></span>
The thymus is a vital role in creating white blood cells.
