Option 1, a Register, is a type of computer memory used to quickly accept, store, and transfer data within a computer`s processing unit. Hence, it`s not related to signal amplification.

Option 2, a Transistor, is the correct answer. It`s a semiconductor device used to amplify or switch electronic signals and electrical power by preserving the shape of the original signal. This ability to preserve the input signal`s form makes it an essential tool in many electronics, including signal amplification.

Option 3, a Flip-flop, is a circuit that has two stable states and can be used to store state information. But it doesn`t have anything to do with signal amplification or maintaining the shape of the original signal.

Option 4, a Diode, only allows current flow in one direction and therefore does not preserve the form of the input signal or amplify it. Instead, it`s more commonly used for tasks like converting AC to DC.