This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Metabolism of nucleic acids, Subject name: Biochemistry
Which of the following base is not found in nucleic acids? 
Select and explain. 
A. Adenine, B. Guanidine, C. Uracil, D. Cytosine
B: Guanidine
Answer: B: Guanidine 
Explanation: Adenine, Guanine, Cytosine, Thymine, and Uracil are Nucleic acids Ref-Harpers illustrated biochemistry 30/e p380