Answer: The option that correctly describes the bolded word is "The word “very” is an adverb describing to what extent".
Step-by-step explanation: An adverb is a word or a phrase used to modify another adverb or other parts of speech such as an adjective or a verb. In the sentence provided, "very" is an adverb because it is modifying an adjective: "beautiful". In that way, "very" is describing the adjective and it is also acting as an intensifier: it indicates to what extent the coral reef was beautiful.