The correct answer is: A. capacitor
An anti-static strap uses a small capacitor to make sure you do not become the least path of resistance to the ground. The capacitor is connected to the ground and to your body, and it helps to equalize the electrical charge between you and the ground. This prevents static electricity from building up on you, which can damage sensitive electronic equipment.
A capacitor is an electrical device that stores energy in an electric field. It consists of two conductive plates separated by an insulator. When a voltage is applied to the capacitor, an electric field is created between the plates. This field stores energy, which can be released when the voltage is removed.
In an anti-static strap, the capacitor is connected to the ground and to your body. When you are wearing the strap, the capacitor helps to equalize the electrical charge between you and the ground. This prevents static electricity from building up on you, which can damage sensitive electronic equipment.
The other options are incorrect because they are not devices that store energy in an electric field. A diode is a semiconductor device that allows current to flow in one direction only. A transistor is a semiconductor device that can be used to amplify or switch electronic signals. A resistor is a passive electrical component that resists the flow of current.
I hope this explanation is helpful!