The correct answer is A. Drain, Gate, Source.
An FET (field-effect transistor) is a type of transistor that uses an electric field to control the flow of current. It has three terminals: drain, gate, and source. The drain is the terminal where the current flows out of the device. The gate is the terminal where the electric field is applied. The source is the terminal where the current flows into the device.
Option B is incorrect because it does not list all three terminals of an FET. Option C is incorrect because it lists the terminals of a vacuum tube, not an FET. Option D is incorrect because it lists the terminals of a bipolar junction transistor, not an FET.