Select the most appropriate option to fill in the blank. Anita wore a ______…

When a blank appears directly before a noun and is meant to describe a quality of that noun, the natural choice is an adjective, since adjectives are the part of speech built specifically to modify nouns; the verb and adverb forms of the same root cannot occupy that position at all. English does allow certain nouns to modify other nouns in fixed attributive compounds (for example "beauty contest"), but the adjective remains the standard, idiomatic choice for directly describing a noun's quality in an open, non-fixed phrase like this one.

In this sentence, the blank sits between the article "a" and the noun "dress", so it must be filled by a word that describes the dress. Of the four forms built on "beauty", "beautiful" is the adjective, so "a beautiful dress" is the grammatically correct phrase.

• "beautify" is a verb (to make something beautiful) and functions as an action, so it cannot modify the noun "dress" that follows the blank.

• "beauty" is a noun (the quality of being beautiful); while some nouns do combine attributively with other nouns in fixed expressions (for example "beauty contest"), "a beauty dress" is not an established or idiomatic English collocation, so it does not correctly complete this sentence.

• "beautifully" is an adverb (describing how an action is carried out) and modifies verbs, not nouns, so it cannot describe "dress" directly.

Checking each option against the noun-modifier rule confirms that only the adjective form fits the blank, making "beautiful" the correct choice.