How is the decision procedure used when comparing two or more mutually exclusive projects on the basis of the rate-of-return measure?

What is (a) the highest, and (b) lowest rate of return (in percent) possible?

Much of the current generation capacity of PEC facilities utilizes coal and natural gas as the primary fuel source. What about the ethical aspects of the government’s allowance for these plants to continue polluting the atmosphere with the emissions that may cause health problems for citizens and further the effects of global warming? What types of regulations, if any, should be developed for PEC (and other generators) to follow in the future?