This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Central Nervous system, Subject name: Pharmacology
In treatment of Parkinsonism, L-Dopa is combined with carbidopa mainly: 
Select and explain. 
A. To decrease the treatment duration, B. To decrease central 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: Administered along with levodopa, they increase its W2 ir. :periphery and make more of it available to cross blood-brain barrier to reach its site of action REF: KD TRIPATHI ESSENTIALS OF MEDICAL PHARMACOLOGY