Answer: The correct answer is "their skin senses it as warmth".
Explanation:
Electromagnetic wave: the direction of electric field and magnetic field are perpendicular to the direction to the propagation of the wave. It travels with the speed of the light.
For example, X-rays, gamma rays, infrared rays and visible region.
Infrared radiation: The range of the wavelength is from 700 nm to 1 mm. It is longer than the visible light. It is a part of the electromagnetic spectrum.
The infrared radiations cannot be seen by naked eyes of human. It can be felt by the human being. They can sense it as heat.
It is given in the problem that most objects emit infrared energy. Human can feel this infrared radiation. Their skin senses it as warmth.
