Final answer:
The adverb in the sentence 'His brother died suddenly while they were on a trip.' is 'suddenly'.
Step-by-step explanation:
The adverb in the sentence 'His brother died suddenly while they were on a trip.' is suddenly. An adverb is a word that modifies a verb, adjective, or other adverb, and it typically provides information about when, where, how, or to what extent an action happened. In this sentence, 'suddenly' provides information about how his brother died while they were on a trip.
Learn more about adverbs