The answer to the question is B.
Answer: Political scientist
Explanation:
Political scientist is the person who studies beginning, development, trend and function of any political system as a finding or research.This study is based on studying political regulation, operations, government policies,political history etc.
According to the question, David should contact political scientist for gaining information about highest expected age-group to vote in election as per their analyzation and study of political system or field and trend.
B. None of these are examples of permissible limitations on the freedom of speech - this is the answer that represents an instance where the government can/or can't limit what people say.