Answer:
B. adjective
Step-by-step explanation:
The infinitive phrase "to be understood by the audience" is used as an adjective in the sentence "Their words were too muffled to be understood by the audience."
An adjective is a word that modifies a noun or pronoun.
In this case, the infinitive phrase modifies the noun "words." It tells us what kind of words they were: words that could not be understood by the audience because they were too muffled.
Here is a breakdown of the sentence:
- Their (possessive pronoun): modifies the noun "words"
- words (noun): the subject of the sentence.
- were (verb): the main verb of the sentence
- too (adverb): modifies the adjective "muffled"
- muffled (adjective): describes the noun "words"
- to be understood by the audience (infinitive phrase): modifies the adjective "muffled"
Therefore, the answer is B. adjective.