What are the three main components of a CRT?

The correct choice highlights the three essential components of a Cathode Ray Tube (CRT): the electron gun, deflection system, and phosphor screen.

The electron gun is responsible for generating and directing a beam of electrons. This beam is emitted from the gun and travels towards the screen. The deflection system, which consists of electromagnetic coils, precisely directs the path of the electron beam across the screen to create images. Without this system, the beam would not reach the appropriate locations on the phosphor screen to form a coherent picture.

Finally, the phosphor screen plays a crucial role in visual output. When the beam of electrons strikes the phosphor-coated surface, it excites the phosphor material, causing it to emit light. This process is what ultimately enables us to see the images on the display. Each component is integral to the functioning of a CRT, working together to convert electrical signals into visible images.

Other options do not accurately represent the fundamental components of a CRT. For example, lenses and casing relate more to optical devices or housing rather than the internal mechanisms that create the display. A power supply and signal processor pertain to the broader electronics that can be found in various display technologies but are not intrinsic components of a CRT itself.