Step 1: Understanding the Question:
The question identifies the historical figure responsible for the foundation of agricultural extension services in the United States.
Step 2: Detailed Explanation:
• 1. Legacy of Seaman A. Knapp: Seaman Asahel Knapp (1833–1911) is universally acknowledged as the "Father of Cooperative Extension" in the United States.
• 2. Demonstration Strategy: His revolutionary idea was that "what a man hears, he may doubt; what he sees, he may possibly doubt; but what he does himself, he cannot doubt." This led to the creation of 'Demonstration Farms,' where farmers learned by doing under expert guidance.
• 3. Smith-Lever Act: His work laid the legislative groundwork for the Smith-Lever Act of 1914, which established the Cooperative Extension Service.
• 4. Other Options: Paul Leagans (Option D) is known as the father of extension *education* (the academic discipline). Spencer Hatch (Option C) and Leonard Elmhirst (Option B) are associated with rural reconstruction work in India (Marthandam and Sriniketan respectively).
• 5. Significance: Knapp's 'Demonstration Method' remains the most effective teaching tool in Home Science and Agricultural extension worldwide today.
Step 4: Final Answer:
Seaman A. Knapp is the father of extension work in the USA.