Answer: A and D.
Answer analysis:
LED displays can be classified into the following categories according to their luminous colors:
A. Monochrome display: This type of display can only display one color of light, usually one of red, green or blue. They are usually used for simple information display, such as text or icons.
B. Dual-primary color display: Although the option says "dual-primary color", the more common term is "dual-color display" or "pseudo-color display". This type of display can display two colors of light, red and green. By adjusting the brightness ratio of the two colors, more colors can be simulated, including yellow. However, it cannot display a true full-color effect.
C. Four-primary color display: In the standard LED display classification, there is no direct category of "four-primary color display". The standard LED display luminous color classification is mainly based on the three primary colors of red, green and blue (RGB). Although some advanced technologies may involve additional color channels (such as white), they are not usually called "four primary colors".
D. Full-color display: This display is capable of displaying a full range of colors, and can produce almost any color through a combination of red, green, and blue (RGB) LED lamp beads. Full-color displays are widely used in advertising, entertainment, sports stadiums, and other fields.
In summary, according to the color of the light, LED displays are mainly divided into monochrome displays, dual-primary color (or dual-color) displays, and full-color displays. Therefore, the correct options are A, a variant of B (although the option is written as dual-primary color, it is more accurate to understand it as dual-color), and D. However, directly based on the content of the options, A and D are clearly correct, B is also correct when understood as a dual-color display, and C (four-primary color display) is not a standard classification.
So, if you have to choose the closest and most accurate answer combination, it should be A and D, but considering that option B is also relevant in a certain understanding, usually in actual situations, we may say that A, B (understood as dual-color), and D are all correct, although B's statement is not the most accurate. But under the strict options of this question, the most accurate answers are A and D.