applications of microwaves

The answer is option (d)

Microwave, which is electromagnetic wave of frequencies between 30 MHz to 300 GHz, is of much lower energy than ultraviolet (frequency about 3x10^15 Hz) or gamma rays. The latter two types of radiation are generally used for sterilization purpose.

[Note: sterilization means the killing of germs and bateria in food without cooking up the food. Thus heating a raw food in a microwave oven, although could kill germs, the food would become cooked, and not to remain raw.]

(d)used to kill germs in sterilization
Researchers soaked sponges and scrubbers in a disgusting brew of raw wastewater containing fecal bacteria, viruses, protozoan parasites and bacterial spores, including Bacillus cereus spores—known for being very hard to kill with heat, chemicals and even radiation.