The voice system allows the speaker to adjust the focus of the proposition, but some verbs bridge the gap between active and passive, known as ergative or labile verbs. Analyze the assertions regarding ergative verbs in English syntax:
I. In the sentence "The window broke," the verb functions intransitively with a passive meaning, despite having active morphology and no explicit agent.
II. Ergative verbs require an agent in the subject position to be grammatically correct in the active voice.
III. "The book reads well" is an example of a middle voice construction where the grammatical subject undergoes the action.
Select the correct analysis: