Hurricane Katrina was the costliest hurricane in US history.

A. Noun

B. Verb

C. Adjective

D. Adverb

C

Which word is underlined?

Costliest

Yes, costliest is an adjective.

To determine the correct answer, we need to identify the function of the word "costliest" in the sentence "Hurricane Katrina was the costliest hurricane in US history." In this sentence, "costliest" describes the hurricane and provides information about its level of cost.

Since it modifies the noun "hurricane," the word "costliest" is an adjective (option C). Adjectives are words that describe or modify nouns or pronouns, providing additional information about them. In this case, "costliest" describes the hurricane as the one with the highest cost in US history.