Final answer:
The phrase 'in a red suit' acts as an adjective phrase in the sentence about Santa Claus because it describes the noun it refers to by providing additional details about Santa Claus's attire. The answer to the student's question is option b) Adjective.
Step-by-step explanation:
The phrase "in a red suit" in a sentence about Santa Claus functions as an adjective phrase. This is because the phrase is providing additional information about a noun, likely "Santa Claus" in the sentence. It describes Santa's suit and gives us more details about what he is wearing, which is the function of an adjective. Therefore, the correct answer to what part of speech the phrase "in a red suit" represents is (b) Adjective.
To further clarify, adjectives are words that describe or modify nouns or pronouns. In the phrase "in a red suit", the word 'red' is an adjective describing the color of the suit, and the entire phrase 'in a red suit' is an adjective phrase qualifying a noun that it is referring to.