Which of the following options is the most suitable conversion of the following sentence into Passive Voice?
Didn't the manager inform all the employees about the new rule?

Correct option is A

The correct option is (a).

Explanation:
The active sentence is an interrogative sentence in the Simple Past tense (Did + Subject + V1). In passive voice, 'did' changes to 'was/were' depending on the new subject. Here, the object 'all the employees' is plural, so 'were' is used. The past participle 'informed' (V3) must follow.

Structure:
Active voice: Did + Subject + V1 + Object?
Passive Voice: Was/Were + Object + V3 + by + Subject?

Why other options are incorrect:
Option B uses 'Wasn't' with a plural subject. Option C keeps 'Didn't' which is incorrect for passive. Option D uses 'Doesn't' which changes the tense to present. So the correct answer is (a)