Which is a key detail about an event in the story

The prefix of the italicized word in the sentence is rather difficult

Based on the cause-and-effect relationship in this sentence, what is the meaning of the word illuminate? the colors and patterns on the stained glass windows were illuminated as thousands of candles burned during the special church service. a) to melt or change form b) to grow taller or wider c) to become extremely hot d) to light up or make clear

This is a set of words that begins with a preposition.