a - Explain the difference between positive and normative questions and give examples for each: b - Explain negative externality and give example(s). c - Explain positive externality and give example(s). d - Explain what Marginal Product of Labor is. e - Explain what Decreasing Marginal Return is. f - Explain what Increasing Marginal Return is. g - Explain what Constant Marginal Return is. h - Explain the Efficiency concept in Economics