(a) Please explain how if the United States gives Covid-19 vaccines for free to poor developing countries, that might result in benefits for both the United States and for the developing countries. Is this an externality for the United States? You must give an explanation. (b) Are Covid -19 vaccines in the United States a public good? Assume that there is no shortage of vaccines in the U.S. and the vaccines are paid for either by the government or by health insurance. Please explain. (c) Are Covid-19 vaccines in India a public good? In India there is a shortage of vaccines, and the public has to pay out-of-pocket for the vaccines. Please explain