Answer: The correct answer is D. Heating by the sun.
Comets are balls composed of dust and ice orbiting around the Sun in elliptical orbits. The orbit of the comet takes it near and far away from the sun. As the comets get closer to the Sun, the heat of the sun vaporizes the materials on the surface of the comet which forms a tail pointing away from the sun.
A comet tail is visible from Earth when they are illuminated by the Sun on approaching the inner Solar System. The solar radiations vaporize the volatile materials of the comet which streams out from the nucleus and carries dust away with it. The pressure due to the Sun’s radiation and solar winds leads to the formation of a tail pointing away from the Sun.
