The answer is a. the troposphere
Proteins help form immunoglobulins, or antibodies, to fight infection. Antibodies are proteins in your blood that help protect your body from harmful invaders like bacteria and viruses. When these foreign invaders enter your cells, your body produces antibodies that tag them for elimination.
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If the arteries become less stretchy, the heart will have to work harder to eject blood.
I think it is true. If it is wrong, I am so sorry.
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