Answer:
purine
Explanation:
Purines are nitrogenous base that have two carbon-nitrogen rings. The most naturally occurring purines are adenine and guanine which are found in DNA and RNA as nucleotide building blocks of these polymers. Purines are constituents other important biomolecules, such as ATP, GTP, cyclic AMP, NADH, and coenzyme A. Purine and pyrimidine ribonucleotides built up essential intermediates in the synthesis of the polynucleotides RNA and DNA.
I think the answer is A, blood would leak backwards through the damaged valves due to gravity, causing lower leg swelling. The main function of the valves in veins is to prevent back flow of blood. Blood in the arteries, after being pumped by the heart, are under much higher pressure than blood in veins so there is no need for arteries to prevent back flow. However, within the veins especially those of legs are valves for the above function, therefore damaged valves would cause some back flow of blood, causing swelling of the legs.
Eve.......................
