Bill Lives in Montana and Likes to Grow Zucchini

Multiple Choice

Bill lives in Montana and likes to grow zucchini. He applies fertilizer to his crop twice during the growing season and notices that the second layer of fertilizer increases his crop but not as much as the first layer. What economic concept best explains this observation?

A) the law of diminishing marginal utility
B) the law of diminishing returns
C) return equalization principle
D) the principal-agent problem