The amino acid Histidine, or His.
I believe the answer is A because this is the two loop system because the air you take in from your lungs automatically is polluted. In the two loop system, the carbon dioxide is taken out out of the oxygen and is pumped back to the heart to be taken out of the body. The oxygenated blood is pumped into places it is needed.
A. A Kilogram is the SI unit used to measure mass.
