Final answer:
The word 'mean' in the given sentence is an adjective, which is used to describe the teacher's nature, making option D) Adjective the correct choice.
Step-by-step explanation:
In the sentence 'The very mean teacher gave all of her students homework and projects every Friday of the school year. Yuck!' the word 'mean' functions as an adjective. An adjective is a word that describes or modifies a noun. In this case, 'mean' is describing the teacher's disposition. This is in contrast to the other parts of speech listed as options, such as pronouns (which replace nouns), verbs (which depict actions or states of being), and nouns (which are persons, places, things, or ideas). Therefore, the correct answer to the question is D) Adjective.