In region second of production with a single variable input

The correct answer is: A. marginal product is declining but non-negative.

In the second region of production, the marginal product of a variable input is declining but non-negative. This means that each additional unit of the variable input produces less output than the previous unit, but it still produces some output. The average product of a variable input is also declining in the second region of production, but it is still positive. This means that the average output per unit of the variable input is decreasing, but it is still greater than zero.

The following is a brief explanation of each option:

• Option A: marginal product is declining but non-negative. This is the correct answer.
• Option B: average product is negative. This is not correct. In the second region of production, the average product of a variable input is still positive.
• Option C: average product is increasing. This is not correct. In the second region of production, the average product of a variable input is declining.
• Option D: average product is positive and marginal product is increasing. This is not correct. In the second region of production, the average product of a variable input is still positive, but the marginal product is declining.