The answer is carbon dioxide. im 100 percent this is right<span />
<span>The metabolic activity of a specific region of the living rat brain can be revealed by measurement of Fos protein concentration.
c-Fos is a proto-oncogene that is the homolog of the retroviral oncogene v-fos. It was first discovered in rat fibroblasts as the transforming gene of the FBJ MSV.</span>
The right answer is D (less responsive to antigens)
It is proven that, after puberty, thymus activity (an organ that is included in the lymphatic system, producing T cells that pick up antigens) decreases and that in adult and aged people the thymus has no role. Work done in humans indicate that in fact the cellularity begins to decline from birth in favor of lymphocyte perivascular spaces and connective and adipose tissue, which leads to a decrease in the capture of antigens.
<span>The group exposed to a newly created drug that is being tested in an experiment is called the experimental group.
Whenever any new drug is formed, it is first experimented then it comes in pharmacies for use. Experimental groups are given variables,one variable is tested at a time. After that experimental group is compared to control group.</span>
