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: Pharmacology
Which of the following is not an antimetabolite ? 
Select and explain. 
A. Methotrexate, B. 5 Fluorouracil, C. Gemcitabine, D. Vincristine
D: Vincristine
Answer: D: Vincristine 
Explanation: None