Which of the following are examples of Pareto-efficient changes?

Which of the following are examples of Pareto-efficient changes? Explain your answers. a. Cindy trades her laptop computer to Bob for his old car. b. Competition is introduced into the electric industry, and electricity rates drop. A study shows that benefits to consumers are larger than the lost monopoly profits. c. A high tax on wool sweaters deters buyers. The tax is repealed. d. A federal government agency is reformed, and costs are cut 23 percent with no loss of service quality.