Step 1: Production Function Properties.
A production function homogeneous of degree one follows Euler's equation:
\[
F(K, L) = K \cdot \frac{\partial F}{\partial K} + L \cdot \frac{\partial F}{\partial L}
\]
Here, \( F(K, L) \) represents output, \( K \) is capital, and \( L \) is labor. The condition \( MP_L>AP_L \) indicates diminishing returns to labor.
Step 2: Evaluation of Options.
- (A) \( MP_L \) will be negative: Incorrect. The marginal product of labor is not negative if the production function yields positive output.
- (B) \( MP_L \) will be zero: Incorrect. Since \( MP_L \) is greater than \( AP_L \), it cannot be zero.
- (C) \( MP_K \) will be negative: Incorrect. Insufficient information is provided to conclude that \( MP_K \) is negative.
- (D) \( MP_L \) and \( MP_K \) will both be negative: Correct. When marginal products are decreasing, both labor and capital can experience negative marginal returns at certain output levels.
Step 3: Conclusion.
The correct option is (D). When the marginal product of labor surpasses the average product, both \( MP_L \) and \( MP_K \) may be negative.