He had been working nicely – Identify the adverb:

1. He
2. Working
3. Nicely
4. Had been

The correct answer is “nicely” because it is the word that modifies the verb phrase “had been working.” It describes the manner of the action, answering the question “How had he been working?” – nicely. An adverb can modify a verb, an adjective, or another adverb. “Nicely” ends in “-ly,” which is a common suffix for adverbs formed from adjectives (nice -> nicely). The other options are incorrect: “He” is a pronoun, “working” is the main verb in its present participle form, and “had been” is an auxiliary verb forming the past perfect continuous tense. None of these modify the action; they are part of the core subject and verb structure of the sentence.