Imagine that you were able to see a nucleotide under a very special microscope. as you scan the nucleotide you see a u nitrogen base. without seeing any other part of the nucleotide you know that

DNA and RNA are the nucleic acids made of large number of repeating sub-units called nucleotides. Each nucleotide consists of a sugar, a phosphate and a nitrogenous base. There are four types of nitrogenous bases such as adenine (A), guanine (G), cytosine (C) and thymine (T) in DNA.  Whereas, in RNA, base thymine is absent and it is replaced by uracil (U). Each base makes one nucleotide with sugar and phosphate.

While scanning the nucleotide one see a u nitrogen base, it means this nucleotide is a part of RNA because nitrogenous base uracil (u) is only present in RNA.  

the answer is otpion c) understanding

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the oxygenated blood then leaves the lungs through pulmonary veins, which return it to the left heart, completing the pulmonary cycle. this blood then enters the left atrium, which pumps it through the mitral valve into the left ventricle. from the left ventricle, the blood passes through the aortic valve to the aorta.

deoxygenated blood leaves through the right ventricle through the pulmonary artery. from the right atrium, the blood is pumped through the tricuspid valve (or right atrioventricular valve), into the right ventricle.