The correct answer is A. A pair of words that describe a noun
Step-by-step explanation:
In terms of function, all adjectives describe or modify places, objects, ideas, people, etc, which are known as nouns. For example, in the sentence "The big house" the adjective is "big" because this describes "the house".
Moreover, adjectives are coordinate if two or even more adjectives describe the same noun. For example in the sentence "The brave, young girl" the adjectives "brave" and "young" are used to describe the noun "girl". Also, in coordinate adjectives, the adjectives are separated by commas. According to this, a coordinate adjective is a pair of words that describe a noun.