Final answer:
The correct vocabulary word to complete the sentence is 'assail,' meaning to attack, fitting the context of doubts troubling the hero. In practicing verb forms, maintain consistent tense usage unless the narrative requires mixing tenses for chronological accuracy. Option d.
Step-by-step explanation:
The vocabulary word that best completes the sentence is 'assail.' The sentence would therefore read: 'Although the hero was confident, doubts would sometimes assail him in the middle of the night.'
The verb 'assail' means to attack or to set upon with force or vigor, and in the context of the sentence, it figuratively refers to the doubts bombarding the hero's mind.
Neither 'resolute' (adjective, meaning determined), 'vehemently' (adverb, meaning passionately or intensely), nor 'infallible' (adjective, meaning incapable of making mistakes) would fit contextually within the sentence.
In practicing effective verb forms, consider the tense throughout the exercise. When a narrative is in the present tense, verbs should consistently reflect actions happening currently. In contrast, for a narrative in the past tense, verbs should reflect actions that have already occurred.
It is also possible to have a mix of tenses if events in the text span across different times.
So Option d.