15. Up To 10,000 Retail Stores Could Close This Year Up to 10,000 U.S. storefronts could disappear by the end of 2021. Consumers prefer the safety of shopping online during the Covid-19 pandemic. Source: CBS News, January 28, 2021 a. Draw the PPF curves for storefront and online retailers before and after the Covid-19 pan- demic. b. Draw the marginal cost and marginal benefit curves for storefront retailers and online retail- ers before and after the Internet became an option. c. Explain how changes in production possibili- ties, preferences, or both have changed the way in which goods are retailed.