Concept:Mass media can send one message instantly to a very large and widespread audience at a low cost per farmer.
Explanation:Urgent information needs to reach thousands of farmers at the same moment with very little delay.
Demonstrations require physical presence and are limited to small groups.
Field trips involve taking farmers to a specific location, which is slow and costly.
Evaluation is a follow-up process, not a method of spreading information to many people at once.
Mass media, such as radio, television, and mobile phone broadcasts, can transmit the same urgent message simultaneously to a very large number of farmers across different locations.
Because the cost is shared over a huge audience, it becomes the most economical and efficient way to deliver urgent agricultural information.
Therefore, mass media is the best choice for cost-effective urgent communication.
Answer:C. mass media