Option 1 -> If TP is constant, MP would be zero (no additional output), not constant.
Option 2 -> If TP is zero, there's no production and MP would also be zero or undefined.
Option 3 -> When MP is constant, each additional unit of input adds the same amount to output, making TP increase linearly.
Option 4 -> If TP decreases at constant rate, MP would be constant but negative, which is unusual in production theory.
Hence, Option 3: Total Product is increasing at a constant rate -> Marginal Product represents the rate of change of Total Product. When MP is constant (say 5 units), each additional input adds exactly 5 units to TP. This creates a linear relationship where TP increases steadily. For example, if MP = 5, then TP might be 5, 10, 15, 20... showing a constant increase of 5 units. Mathematically, if MP = dTP/dL = k (constant), then TP = kL + c, which is a linear function indicating constant rate of increase. -> correct