The correct answer is D. Vds > Vgs – Vt.
Saturation is a condition in which the drain current of a MOSFET is limited by the maximum current that can flow through the device. This occurs when the gate-source voltage (Vgs) is greater than the threshold voltage (Vt) and the drain-source voltage (Vds) is greater than Vgs – Vt.
When Vgs is greater than Vt, the MOSFET is turned on and current can flow from the drain to the source. The amount of current that flows is proportional to the difference between Vgs and Vt. As Vds increases, the current that flows through the MOSFET also increases. However, once Vds reaches Vgs – Vt, the current that flows through the MOSFET reaches a maximum value. This is because the gate-source voltage is no longer able to increase the current that flows through the device.
Saturation can be a problem in some applications, as it can limit the amount of power that can be delivered by the MOSFET. However, it can also be used to advantage in other applications, such as when a constant current source is needed.