Final answer:
a. akinesia. The negative symptom of Parkinson's disease is akinesia, which is the loss or reduction of voluntary muscle movement.
Step-by-step explanation:
The negative symptom of Parkinson's disease is akinesia, which is the loss or reduction of voluntary muscle movement. Akinesia can cause a person to have difficulty initiating and maintaining movement. This symptom is characterized by a lack of facial expression, reduced arm swing while walking, and a stooped posture.