Concept:Introducing a new crop variety to farmers works best through practical, direct methods that are easy to observe and understand.Explanation:Demonstrations allow farmers to see the new rice variety growing and performing in real conditions.Field trips help farmers visit successful farms and observe the actual benefits of the new variety.Farmers’ cooperative societies are a useful channel for sharing information through meetings and group discussions.Circular letters are inappropriate because many farmers may not be able to read them, and written messages are less effective than practical methods for introducing new farming practices.Answer:B. Circular letters