The correct answer is: A. x-axis at one.
The slope coefficient of a cost function is the amount by which the cost changes for each unit change in output. If the slope coefficient is zero, then the cost function is a horizontal line. This means that the cost does not change as output changes. In other words, the cost is constant.
The x-axis represents the output, and the y-axis represents the cost. If the cost function intersects the x-axis at one, then the cost is always one, regardless of the output. This means that the slope coefficient is zero.
The other options are incorrect because they do not describe a cost function with a slope coefficient of zero. Option B states that the cost function intersects the y-axis at a constant. This means that the cost is always the same, regardless of the output. This is not possible, because the cost must change as output changes. Option C states that the cost function intersects the x-axis at a constant. This means that the output is always the same, regardless of the cost. This is also not possible, because the output must change as the cost changes. Option D states that the cost function intersects the y-axis at one. This is the same as option B, and it is also incorrect.