What kind of display device has pixels that are filled with a liquid crystal compound?

The correct choice is based on the fundamental technology behind the types of display devices listed. LCD, or Liquid Crystal Display, is specifically designed using liquid crystal compounds to manipulate light and create images. In an LCD, the liquid crystals do not emit their own light but instead modulate the light that is passed through them from a backlight. This design allows for a lightweight and energy-efficient display that can produce high-quality images.

In contrast, LED displays use light-emitting diodes that can produce brightness and color directly, while Plasma displays utilize a gas to produce images, which involves a different mechanism entirely. CRT, or Cathode Ray Tube, is an older display technology that relies on electron beams and phosphorescent compounds rather than liquid crystals. Therefore, the presence of liquid crystal compounds uniquely identifies LCDs as the correct answer for the type of display device mentioned in the question.