The correct answer is B.
A profit-maximizing monopolist in separate markets will adjust his sales in each market so that his MR is equal to his MC. This is because the monopolist will want to produce at the point where marginal revenue is equal to marginal cost, which is the point of profit maximization.
Statement 1 is incorrect because the monopolist will not adjust his sales in each market to just equal his MC. Instead, he will adjust his sales in each market so that his MR is equal to his MC.
Statement 2 is incorrect because the monopolist will adjust his sales in each market.
Statement 3 is correct because the monopolist will adjust his sales in each market.
Statement 4 is incorrect because the monopolist will adjust his sales in each market so that his MR is equal to his MC, not less than his MC.