To determine the type of charge carriers that mainly control current in a Field Effect Transistor (FET), we need to understand how a FET operates.

A Field Effect Transistor is a type of transistor that regulates the flow of electrons (or holes) in a semiconductor channel using an electric field. There are two main types of FETs:

• Junction FET (JFET)
• Metal-Oxide-Semiconductor FET (MOSFET)

In both JFETs and MOSFETs, the operation is primarily carried out by the majority charge carriers:

• N-channel FET: Here, electrons are the majority carriers.
• P-channel FET: Here, holes are the majority carriers.

The FET operates by controlling the width of the channel through which the majority carriers flow, thereby controlling the current. This is achieved by applying a voltage to the gate, which modulates the conductivity of the channel.

Now, let's analyze the provided options to determine the correct one:

1. Electrons and holes together: This is not correct because FET operation is primarily controlled by one type of charge carrier, either electrons or holes, but not both simultaneously.
2. Minority carriers only: This is incorrect as FETs predominantly rely on majority carriers to conduct current.
3. Both minority and majority carriers: This is incorrect as FET operation does not involve both types at the same time.
4. Majority carriers only: This is the correct answer because FET operation hinges on the flow of majority carriers within the channel.

Therefore, the correct answer is Majority carriers only.