Assuming a Product Can Be Manufactured Competitively Without Any Externalities

Assuming a product can be manufactured competitively without any externalities at an efficient quantity of 500 units and an efficient price of $150.00 per unit, what efficient quantity-price net subsidy combination would be consistent with a corrective subsidy for a positive externality?

A) 500 units, $150.00 per unit price net subsidy.
B) 300 units, $120.00 per unit price net subsidy.
C) 600 units, $160.00 per unit price net subsidy.
D) 700 units, $100.00 per unit price net subsidy.