To answer this question we need to analyze each available option:
Burning clothing: This method was used during great plagues such as smallpox or the black death, so this cannot be.
Storing water in copper containers: Copper is known for its antibacterial properties, so it was used to store water.
Salting food: This is a very ancient method to preserve food, especially meat so this cannot be.
Microwaving food: microwave kill many microorganisms, however, it was designed primarily to heat food and is still used mainly for this purpose, also is a modern invention so this is the correct answer.
