Final answer:
To safely connect a three-wire power tool to a two-wire receptacle, use an adapter and connect the safety ground wire to the tool's case to prevent electric shock.
Step-by-step explanation:
To safely connect a power tool with a three-wire system to a two-wire receptacle, you should use an adapter with an external ground wire. The correct action among the provided options is to connect the safety ground wire of the adapter to the tool case. This ensures that if there's any fault, the ground wire provides a low-resistance path to the earth, reducing the risk of electric shock. The ground wire is typically green but may also be yellow or a bare wire. Importantly, always ensure the safety ground is connected before plugging in the tool.
A three-wire system includes live/hot, neutral, and ground wires. The grounding of the neutral wire and the case of an appliance or tool ensures that in case of a fault, such as worn insulation that allows the hot wire to contact the case, the circuit breaker will trip, preventing potential electric shocks.