This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Biochemistry
First carbon of pentose sugar of nucleic acid joins 
Select and explain. 
A. N-9 of pyrimidine, B. N-1of pyrimidine, C. N-1 of purine, D. None of the above
B: N-1of pyrimidine
Answer: B: N-1of pyrimidine 
Explanation: Pentose sugar present in DNAs is deoxyribose and in RNAs it is ribose. A pentose sugar (ribose or deoxyribose) is linked to a nitrogenous base (purine or pyrimidine) covalent N-glycosidic bond to form nucleoside. This linkage joins the Carbon-I of pentose sugar with nitrogen-9 of the purine base or nitrogen-I of pyrimidine base.