Final answer:
In the sentences provided, 'good' functions as an adjective, 'usefully' as an adverb, and 'used' as a verb. The context dictates the part of speech, which defines the grammar and meaning of each sentence.
Step-by-step explanation:
In each sentence presented, the forms of the word use vary between verb, adverb, noun, and adjective:
- "I'm feeling good" employs good as an adjective, describing the noun feeling.
- The text usefully acknowledges its sources uses usefully as an adverb, modifying the verb acknowledges.
- "I think somebody already used this fork" utilizes used as a verb, describing the action performed on the noun fork.
Understanding the context helps determine the correct part of speech, which can affect the meaning and function of a sentence. For instance:
- Used is a verb in the past tense.
- Usefully is an adverb describing how something is done.