Answer:
D. "My presentation on our local senior center will convince you to volunteer."
Explanation:
Ok, I admit, this one is tricky, and not everyone is good at context clues. However, I think D is the best answer for a few reasons.
1. "My presentation on our local senior center will convince you to volunteer."
An inference can be draw from that dependant clause that the purpose is to convince the audience to volunteer.
2. "My presentation on our local senior center will convince you to voluneteer."
This is pointing to the audience being of a specific grouping, whether that be a neighborhood, a town, or even a group of towns.
Hope I helped! Let me know if you need me to clarify anything.