Select the correct passive voice form of the given sentence.

Will the manager approve the proposal?

The correct option is Will the proposal be approved by the manager?.

To convert an interrogative sentence in the Simple Future Tense from active voice to passive voice, follow these rules:
1. Identify sentence components:
- Auxiliary Verb: "Will"
- Subject: "the manager"
- Main Verb: "approve" (base form)
- Object: "the proposal"

2. Structure for passive voice interrogatives in Simple Future Tense:
- Active Voice: Will + Subject + Verb (base form) + Object?
- Passive Voice: Will + Object + be + Past Participle (V3) + by + Subject?

3. Formulate the passive sentence:
- Retain the auxiliary verb "Will" at the beginning of the question.
- Shift the object "the proposal" to the position following "Will".
- Add "be" followed by the past participle form of "approve", which is "approved".
- Add the preposition "by" followed by the agent "the manager".

Combining these elements results in: "Will the proposal be approved by the manager?"