Step 1: Understanding the Concept:
The verb ``let'' is a causative verb that follows unique grammatical rules in English.
In the active voice, ``let'' is followed by an object and a bare infinitive (a verb without ``to'').
Example: ``They let him {go}.'' (Not ``to go'').
When converting ``let'' to the passive voice, it retains the bare infinitive. This often sounds awkward to non-native speakers, but it is the strictly correct grammatical form.
Step 2: Detailed Explanation:
Breakdown of the active sentence: ``They (Subject) + let (Verb) + the prisoner (Object) + leave (Bare Infinitive) + early (Adverb).''
To convert to passive:
1. Move the object ``the prisoner'' to the subject position.
2. Use the correct form of ``to be'' for the simple past tense (was/were). Since ``the prisoner'' is singular, use ``was.''
3. Use the V3 (past participle) of ``let.'' Note: the three forms of let are {let-let-let}.
4. Retain the bare infinitive ``leave.''
Result: ``The prisoner was let leave early.''
Analyzing the Distractors:
- Option (B) incorrectly adds ``to'' before ``leave.'' While most passive verbs take a ``to-infinitive,'' ``let'' does not.
- Option (C) uses the synonym ``allowed.'' While this is a common way to avoid using ``let'' in the passive, the word ``allow'' requires a full infinitive (``to leave''). Since the ``to'' is missing in Option (C), it is ungrammatical.
- Option (D) is a redundant and overly wordy construction that does not follow standard passive rules.
Step 3: Final Answer:
Option (A) is the only sentence that correctly applies the bare infinitive rule associated with the verb ``let'' in its passive form.