Provide your best answer for the following question. Give ONLY the answer, no other words or explanation.
For example:

Answer: <most likely answer, as short as possible; not a complete sentence, just the answer!>.

The question is: Signs in many stores and restaurants warn that microwaves are in use. What is the main reason for this warning?
Some people have pacemakers that may be affected by microwaves.
Prevention of burns.