The correct answer is A. The outer metallic body of the appliance.
The earth wire is connected to the outer metallic body of the appliance to provide a safe path for current to flow in the event of a fault. If there is a fault and current flows through the outer metallic body of the appliance, the earth wire will carry the current to the earth and prevent the user from being shocked.
Option B is incorrect because the fuse is not connected to the earth wire. The fuse is connected to the live wire and the neutral wire. The fuse is designed to blow if there is a fault and current flows through it. This will stop the current from flowing and prevent the appliance from overheating.
Option C is incorrect because the filament is not connected to the earth wire. The filament is the part of the appliance that heats up to produce heat or light. The filament is made of a material that has a high resistance to electricity. When current flows through the filament, it heats up.
Option D is incorrect because short circuitry is not a connection. Short circuitry is a fault that occurs when there is a direct connection between the live wire and the neutral wire. This can cause a large amount of current to flow and can damage the appliance.