Concept:To change an active voice sentence with a modal verb in negative interrogative form to passive voice, keep the modal at the start, then place the object, add "be", and the past participle of the main verb, followed by "by" and the original subject.
Explanation:The active sentence is: "Couldn't the mechanic identify the problem?"
Here, "couldn't" is the modal, "the mechanic" is the subject, "identify" is the base verb, and "the problem" is the object.
Step 1: Keep the modal "Couldn't" at the beginning.
Step 2: Replace the subject with the object "the problem".
Step 3: Add the helping verb "be" after the modal.
Step 4: Change the main verb to its past participle form "identified".
Step 5: Add "by" and then the original subject "the mechanic".
The correct passive sentence is: "Couldn't the problem be identified by the mechanic?"
Option A changes the modal to "can't", which is wrong.
Option C omits "be", making it incomplete.
Option D uses "identify" instead of "identified".
Only option B follows the correct structure.
Answer:Option B: Couldn't the problem be identified by the mechanic?