Verified Answer :

c. groups that take and analyze public polls.

The Gallup Organization is independent polling firm in the USA.  Zogby International is a polling firm that operates worldwide. Louis Harris and Associates is a market research and consulting firm. Yankelovich Partners is a polling firm that specializes in consumer trends and lifestyle.

Question: Gallup, Harris, Zogby, and Yankelovich are

Answer: c. groups that take and analyze public polls.