The correct answer is: D. their minimum level.
The marginal cost (MC) curve cuts the average variable cost (AVC) and average total cost (ATC) curves at their minimum level. This is because the MC curve represents the additional cost of producing one more unit of output, while the AVC and ATC curves represent the average cost of producing all units of output. When the MC curve cuts the AVC and ATC curves, it means that the additional cost of producing one more unit of output is equal to the average cost of producing all units of output. This is the point at which the firm is producing at its most efficient level.
The MC curve cuts the AVC curve at the point where the AVC curve is at its minimum level. This is because the MC curve represents the additional cost of producing one more unit of output, while the AVC curve represents the average variable cost of producing all units of output. When the MC curve cuts the AVC curve, it means that the additional cost of producing one more unit of output is equal to the average variable cost of producing all units of output. This is the point at which the firm is producing at its most efficient level in terms of variable costs.
The MC curve cuts the ATC curve at the point where the ATC curve is at its minimum level. This is because the MC curve represents the additional cost of producing one more unit of output, while the ATC curve represents the average total cost of producing all units of output. When the MC curve cuts the ATC curve, it means that the additional cost of producing one more unit of output is equal to the average total cost of producing all units of output. This is the point at which the firm is producing at its most efficient level in terms of both variable and fixed costs.