Question

what heats the suns corona to high temperatures?
long - wavelength electromagnetic radiation emitted by layers below
fluctuating magnetic fields from below that transport energy outward
visible light emitted by layers below
short - wavelength electromagnetic radiation emitted by layers below
sun - grazing comets giving up their energy of motion as they vaporize in these two layers

Explanation:

The Sun's corona is heated by energy from below. Long - wavelength electromagnetic radiation (like infrared) doesn't have enough energy to heat the corona to millions of degrees. Visible light also doesn't carry sufficient energy for such high - temperature heating. Short - wavelength electromagnetic radiation (e.g., X - rays) is a result of high - temperature processes in the corona, not the cause. Sun - grazing comets are too rare and their energy contribution is negligible. Fluctuating magnetic fields (magnetic reconnection and wave - heating mechanisms) from the Sun's interior transport energy outward and can heat the corona.

Answer:

fluctuating magnetic fields from below that transport energy outward