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: Physiology
Replacing alanine by which amino acid will increase UV absorbance of protein at 280nm wavelength: 
Select and explain. 
A. Leucine, B. Proline, C. Arginine, D. Tryptophan
D: Tryptophan
Answer: D: Tryptophan 
Explanation: Tryptophan