Brain is the organ that is most sensitive to the absence of glucose in the blood. The glucose is needed by the neurons in the brain to carry out their functions. The neurons when deprived of glucose, start to slow down and die out of exhaustion. The lack of glucose can cause symptoms of hypoglycemia, wherein a person starts to experience hallucinations and suffers from excruciating pain in the joints of the bones.
D. A keystone species existence keeps an ecosystem in balance.
DNA is a polymer that contains deoxyribose and a phosphate backbone. It contains these 4 nitrogenous bases: Adenine, Guanine, Cytosine and Thymine.
RNA on the other hand is a polymer that contains ribose and phosphate backbone. It contains 4 nitrogenous bases of: Adenine, Guanine, Cytosine and Uracil.
Hope that helps a bit.
C.) The prefix pro means to advance, in this case the promoter is the chemical that starts the replication
