If the marginal output is positive, total output will

The correct answer is A. increase.

Marginal output is the additional output produced when one more unit of input is added. If marginal output is positive, then adding one more unit of input will result in an increase in total output.

Option B is incorrect because if marginal output is negative, then adding one more unit of input will result in a decrease in total output.

Option C is incorrect because if marginal output is constant, then adding one more unit of input will not result in a change in total output.

Option D is incorrect because if marginal output is zero, then adding one more unit of input will not result in any output.