Answer:
Infrared Waves
Step-by-step explanation:
Since electromagnetic waves are of different energy range is used for different works
Higher energy range electromagnetic waves are not good to expose for human so we can not use them for warming purpose as they are dangerous.
So X rays and Gamma rays can not be used
Also radio waves are of least energy so they can not be used for the purpose of warming.
So correct answer for the replacement of microwaves is infrared waves because they have sufficient energy that can be used to warm up.