Why Would the Efficacy of Levodopa Decrease Over Time

Why would the efficacy of levodopa decrease over time?

A) Long-term use of levodopa creates a tolerance to the drug,decreasing its efficacy.
B) Progressive desensitization of DA receptors requires an increased amount of DA to produce therapeutic effects.
C) The mechanism by which levodopa is metabolized eventually becomes compromised because its constant levels in the brain decrease its efficacy.
D) Levodopa eventually causes liver damage and is unable to be completely metabolized in the body decreasing its efficacy.