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: Microbiology
Growth factor needed for salmonella - 
Select and explain. 
A. Tryptophan, B. Niacin, C. B-12, D. Citrate
A: Tryptophan
Answer: A: Tryptophan 
Explanation: Ans. is 'a' i.e., Tryptophan