Which of the following is a good technique when using a fire extinguisher?

Directing the extinguisher at the base of the flames using a sweeping motion is the recommended technique for effectively putting out a fire. This approach ensures that the extinguishing agent makes contact with the source of the fire, which is where the combustion is taking place. By aiming at the base, you are able to cut off the fuel supply and suppress the fire at its origin.

Additionally, using a sweeping motion allows for broader coverage of the flames, enhancing the chances of extinguishing the fire completely. This technique not only helps in controlling the fire but also prevents it from spreading. The other methods, such as spraying directly at the flames or aiming at the top, may not effectively reach the fuel and can potentially allow the fire to continue burning or spread. Shaking the extinguisher before use is unnecessary and could lead to confusion and mishandling during a critical moment.