The correct answer is: A. nMOS depletion
A depletion-mode MOSFET is a type of MOSFET in which the channel is initially depleted of charge carriers when no voltage is applied to the gate. This means that the threshold voltage for a depletion-mode MOSFET is negative.
An enhancement-mode MOSFET is a type of MOSFET in which the channel is initially undepleted of charge carriers when no voltage is applied to the gate. This means that the threshold voltage for an enhancement-mode MOSFET is positive.
A pMOSFET is a type of MOSFET in which the channel is made of p-type semiconductor material. A nMOSFET is a type of MOSFET in which the channel is made of n-type semiconductor material.
The threshold voltage is the minimum gate voltage required to turn on a MOSFET. For a depletion-mode MOSFET, the threshold voltage is negative. This means that the gate must be biased negatively with respect to the source in order to turn on the device. For an enhancement-mode MOSFET, the threshold voltage is positive. This means that the gate must be biased positively with respect to the source in order to turn on the device.
The threshold voltage is an important parameter for MOSFETs because it determines the operating point of the device. The threshold voltage is also affected by the temperature and the manufacturing process.