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: Biochemistry
Guanidine group is present in 
Select and explain. 
A. Histidine, B. Proline, C. Tryptophan, D. Arginine
D: Arginine
Answer: D: Arginine 
Explanation: Amino acid  
Special group








Histidine


Imidazole




Proline


Imino group / Pyrrolidine group




Tryptophan


Indole




ariginine


Guanidine group




Phenylalanine


Benzene ring




Tyrosine


Phenol.