This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Nucleotides, Subject name: Biochemistry
Which of the following amino acid is used in biosynthesis of purines? 
Select and explain. 
A. Alanine, B. Glycine, C. Threonine, D. Ornithine
B: Glycine
Answer: B: Glycine 
Explanation: Purine Pyrimidine