Final answer:
The first step in using a fire extinguisher is removing the locking pin. Then, squeeze the handle to discharge the extinguishing agent.
Step-by-step explanation:
The correct first step in using a fire extinguisher to put out a fire is to remove the locking pin. This pin keeps the handle from being accidentally pressed, so it needs to be taken out before using the extinguisher. After removing the pin, you can then proceed to squeeze the handle to release the extinguishing agent. It is important to aim at the base of the fire and sweep from side to side to extinguish the flames.
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