This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Metabolism of nucleic acids, Subject name: Biochemistry
Best radiolabelled marker for DNA replication is 
Select and explain. 
A. Ribose, B. Thymidine, C. Phosphate, D. Uracil
B: Thymidine
Answer: B: Thymidine 
Explanation: Nucleic acids are readily labeled with tags that facilitate detection or purification. A variety of enzymatic or chemical methods are available to generate nucleic acids labeled with radioactive phosphates, fluorophores, or nucleotides modified with biotin or digoxygenin for example.