The working of microwave oven involves:
A. Absorption of microwaves by matter.
B. Reception of microwaves by optical fibre.
C. Microwave amplification by stimulated emission of radiation.
D. Transmission of microwaves through a metal.

Hint: Microwaves are electromagnetic waves which lie in a part of the electromagnetic spectrum which is sandwiched between radio waves and infrared waves. Its wavelength lies between 30 to 0.03 cm. These are used in microwave ovens to efficiently heat food. It heats the food evenly through the matter and it is a quick way to cook food. These days this phenomenon is widely used to heat up the food without much energy loss.

Complete answer:
The simple answer to this statement lies in the fact that energy from microwaves gets absorbed by the water present inside the food molecules. Due to this energy absorption, the molecules of water start vibrating with a frequency, called resonant frequency. Resonant frequency is the frequency which results in maximum amplitude of oscillation of water molecules. In order to design the microwave ovens, we have to make sure that the efficiency of the device is high. Hence we match the frequency of microwaves to the resonating frequency of water molecules to ensure maximum amplitude to produce maximum movement of the molecules to heat the food faster.

So, the correct answer is “Option A”.

Note:
It must be noted that microwaves are not heat waves. They don’t carry heat along with them. They just increase the entropy of polar molecules present in food. Polar molecules means having some dipole moment eg. Water. If we place plastic or ceramic utensils inside a microwave oven, it will remain at room temperature because of no polar molecules. This is also an advantage of using a microwave oven that utensils remain at normal temperature and food becomes hot.