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: Pathology
The gene responsible for folic acid transpo is situated on: 
Select and explain. 
A. Chromosome 10, B. Chromosome 5, C. X Chromosome, D. Chromosome 21
D: Chromosome 21
Answer: D: Chromosome 21 
Explanation: . Chromosome 21