This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Proteins and Amino Acids, Subject name: Biochemistry
Methionine is synthesised in human body from - 
Select and explain. 
A. Cysteine, B. Homocysteine, C. Cystine, D. Tryptophan
B: Homocysteine
Answer: B: Homocysteine 
Explanation: Ans. is 'b' i.e., Homocysteine* Homocysteine in the presence of methionine synthase and methyl B12, gets converted to methionine.