This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: General anatomy, Subject name: Anatomy
Guanidine special group is presesnt in 
Select and explain. 
A. Arginine, B. Proline, C. Tryptophan, D. Tyrosine
A: Arginine
Answer: A: Arginine 
Explanation: AMINO ACID SPECIAL GROUP Arginine Guanidinium Proline Pyrolidine Tryptophan Indole Phenylalanine Benzene Tyrosine Phenol Histidine Imidazole Methionine Thioether linkage Reference: Harpers illustrated biochemistry 30th edition