Answer:
a. equal to its marginal cost and grant a subsidy to cover the loss
Explanation:
In a competitive market there is allocative efficiency non fixing of prices.
The price of commodity is equal to it's marginal cost.
A socially optimal level of output is produced thereby demand will equal marginal cost.
A monopolist however will not set price that is equal to marginal cost normally. Instead they will less goods at a higher cost and charge higher price on it.
If a government wants to regulate a monopoly the best option will be for the monopolist to set a price equal to its marginal cost and government grant a subsidy to cover the loss