A Competitive Firm Will Maximize Profit by Producing the Level

A competitive firm will maximize profit by producing the level of output at which

A) the last unit of output produced adds the same amount to total revenue as to total cost.
B) the additional revenue from the last unit of output produced exceeds the additional cost of the last unit by the largest amount.
C) the firm's total revenue exceeds total cost by the largest amount.
D) both a and b
E) both a and c