You Are a Scientist at a Pharmaceutical Company

You are a scientist at a pharmaceutical company.You know that treating Parkinson's disease patients with dopamine has been ineffective in the past,however,your company has recently developed a method to modify drugs that can help them cross the blood-brain barrier.If you modified dopamine in this way,would it make dopamine treatment of Parkinson's more effective?

A) No,because acetylcholine is the main neurotransmitter that is deficient.
B) No,because injecting dopamine only makes the substantia nigra down-regulate its own production of dopamine.
C) No,because dopamine will be broken down in the body before reaching the brain.
D) Yes,a central issue with dopamine treatment is that dopamine cannot cross the blood-brain barrier.