Which of the Following Must Occur for Wind and Solar

Which of the following must occur for wind and solar power to displace coal and gas?

A) Wind and solar producers must reduce the marginal cost of energy storage to below the marginal cost of using coal and gas.
B) Government must continue to subsidize wind and solar power and heavily tax energy generated using coal and gas.
C) Wind and solar producers must improve the ability of turbines and solar panels to generate power.
D) Government must require that all wind and solar power plants be located in windy and sunny places, respectively.