The correct answer is d, Ap of labour is at minimum.

When the MP (marginal product) of labor is rising, it means that each additional unit of labor is adding more output than the previous unit. This indicates increasing productivity and efficiency.

When the MP of labor is minimum, it means that each additional unit of labor is adding the least amount of output compared to previous units. This suggests diminishing returns to labor, where adding more labor does not result in significant increases in output.

The AP (average product) of labor is calculated by dividing the total output by the number of units of labor. When the AP of labor is at its minimum, it means that the average output per unit of labor is the lowest. This indicates that the overall productivity of labor is not optimal.

Therefore, the correct answer is d, Ap of labour is at minimum.