9. Consider there is depletable energy and renewable energy, when would renewable energy be used (assume that the consumers have no preference between the two energies)? O a. C. When the depletable energy is exhausted. O b. B. Whenever the marginal cost of renewable energy is lower than that of depletable energy, with at least some consumers' WTP higher than the renewable energy's marginal cost. O c. D. When the government gives subsidies to renewable energy producers. O d. None of the rest O e. A. After the marginal cost of renewable energy is lower than that of depletable energy