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
In treatment of Parkinsonism, L–Dopa is combined with carbidopa mainly : 
Select and explain. 
A. To decrease dose requirement of L–Dopa, B. To decrease side effects of L–Dopa, C. To decrease effectiveness of L–Dopa, D. To increase crossing of L–Dopa through BBB
D: To increase crossing of L–Dopa through BBB
Answer: D: To increase crossing of L–Dopa through BBB 
Explanation: None