Step 1: Understanding the Concept:
Extension communication channels: individual contact methods (personal interview, farm visit), mass contact methods (newspapers, TV, radio), and group contact methods (field trips, method/result demonstrations, workshops).
Step 2: Detailed Explanation:
Classification of Extension Teaching Methods by number of contacts:
1. Group Contact Methods (D): Involves direct interactive communication with a defined group of 20 to 50 farmers/fishers. Key examples include Field Trips (Study Tours Farm Walks), Method Demonstrations, Result Demonstrations, Group Discussions, Workshops, and Symposia.
2. Individual Contact Methods: Personal Farm Visits (C), Home Visits, Personal Interviews (B), Office Calls, and Telephone Contacts (1-on-1 contact).
3. Mass Contact Methods: Newspapers (A), Radio, Television, Bulletins, Farm Exhibitions, and Social Media ($> 100$s/thousands).
Step 3: Final Answer:
Hence, Field trip is a group contact method, corresponding to option (D).