The correct answer is C. bright.
Radiant colors are bright and vivid. They are often used to create a sense of excitement, energy, or happiness. Delicate colors are soft and muted. They are often used to create a sense of calm, peace, or serenity. Dull colors are lifeless and uninteresting. They are often used to create a sense of boredom, sadness, or despair. Rare colors are uncommon and unusual. They are often used to create a sense of mystery, intrigue, or danger.
In the context of the question, “This painting is full of radiant colors,” the correct answer is C. bright. This is because radiant colors are bright and vivid, which is consistent with the description of the painting. The other options are incorrect because they do not accurately describe the colors in the painting.