Why should you avoid working inside of a CRT?

One of the common warnings posted on the outside of a cathode ray tube monitor is “No user serviceable parts inside.” Why is it a good idea to avoid poking around on the inside of a CRT?

A) CRT monitors contain dangerous chemicals

B) CRT monitors get very hot

C) CRT monitors maintain high voltages, even when unplugged

D) CRT monitors are very fragile and can easily break