**Rule**: For a negative sentence in the Past Continuous Tense, the passive voice structure is **Object + was/were + not + being + V3 + by + Subject**.

- **Correct Answer (c)**: The object 'such a result' becomes the subject. The passive verb form 'was not being expected' correctly reflects the negative Past Continuous tense.
- **Incorrect Answer (a)**: This incorrectly changes the tense to Simple Past.
- **Incorrect Answer (b)**: This incorrectly changes the tense to Present Perfect.
- **Incorrect Answer (d)**: This incorrectly changes the tense to Present Continuous.

**Rule**: When the active sentence uses 'has to'/'have to', the passive form is **Object + has/have to + be + V3**. The choice between 'has' and 'have' depends on the new subject.

- **Correct Answer (d)**: The object 'all the details' becomes the subject. Since 'details' is plural, it takes 'have to be', followed by the past participle 'checked'.
- **Incorrect Answer (a)**: 'have been checked' is the passive of the Present Perfect Tense.
- **Incorrect Answer (b)**: 'are to be' implies a plan, not the necessity of 'have to'.
- **Incorrect Answer (c)**: 'had to be' incorrectly changes the tense to the past.

**Rule**: For an interrogative sentence in the Simple Past Tense starting with 'Which', the passive structure is **Which + noun + was/were + V3 + by + subject?**

- **Correct Answer (c)**: 'Which route' remains at the beginning. As 'route' is singular, it is followed by 'was' and the past participle 'taken'.
- **Incorrect Answer (a)**: This incorrectly changes the tense to Simple Present.
- **Incorrect Answer (b)**: This incorrectly changes the tense to Present Perfect.
- **Incorrect Answer (d)**: This incorrectly changes the tense to Past Continuous.

**Rule**: For a sentence in the Simple Past Tense, the passive voice structure is **Object + was/were + V3 + by + Subject**.

- **Correct Answer (b)**: The object 'several trees' becomes the subject. Since 'trees' is plural, 'were' is used, followed by the past participle 'uprooted'.
- **Incorrect Answer (a)**: This incorrectly changes the tense to Simple Present.
- **Incorrect Answer (c)**: This incorrectly changes the tense to Past Continuous.
- **Incorrect Answer (d)**: This incorrectly changes the tense to Present Perfect.

**Rule**: For an interrogative sentence in the Simple Past Tense starting with 'Did', the passive structure is **Was/Were + object + V3 + by + subject?**

- **Correct Answer (c)**: The object 'your proposal' is singular, so the sentence starts with 'Was'. This is followed by the object and the past participle 'approved'.
- **Incorrect Answer (a)**: This incorrectly changes the tense to Present Perfect.
- **Incorrect Answer (b)**: This incorrectly changes the tense to Simple Present.
- **Incorrect Answer (d)**: This is not in the correct interrogative word order; the auxiliary verb 'Was' must come before the subject.

**Rule**: For a Present Continuous Tense sentence, the passive structure is **Object + is/am/are + being + V3 + by + Subject**.

- **Correct Answer (d)**: The object 'me' becomes the subject 'I'. The verb form 'am being bothered' is correct for the Present Continuous passive for the first person singular.
- **Incorrect Answer (a)**: This incorrectly changes the tense to Simple Present.
- **Incorrect Answer (b)**: This incorrectly changes the tense to Past Continuous.
- **Incorrect Answer (c)**: This incorrectly changes the tense to Present Perfect.

**Rule**: Interrogative sentences in the Present Continuous Tense starting with 'Who' are converted to passive voice using **By whom + is/am/are + object + being + V3?**

- **Correct Answer (b)**: 'Who' becomes 'By whom'. The object 'the new bridge' is singular, so 'is' is used, followed by the object, 'being', and the past participle 'designed'.
- **Incorrect Answer (a)**: This incorrectly changes the tense to Present Perfect.
- **Incorrect Answer (c)**: This incorrectly changes the tense to Past Continuous.
- **Incorrect Answer (d)**: This incorrectly changes the tense to Simple Present.

**Rule**: For a sentence in the Simple Past Tense, the passive voice structure is **Object + was/were + V3 + by + Subject**.

- **Correct Answer (c)**: The object 'the students' proposal' becomes the subject. Since 'proposal' is singular, 'was' is used, followed by the past participle 'accepted'.
- **Incorrect Answer (a)**: This incorrectly changes the tense to Simple Present.
- **Incorrect Answer (b)**: This incorrectly changes the tense to Past Continuous.
- **Incorrect Answer (d)**: This incorrectly changes the tense to Present Perfect.

**Rule**: In a complex sentence, only the clause with a transitive verb and object is changed to passive. The main clause 'They were watching a movie' (Past Continuous) is passivized, while the subordinate clause remains unchanged. The agent 'by them' can be omitted.

- **Correct Answer (b)**: The object 'a movie' becomes the subject. The verb form 'was being watched' is the correct passive for the Past Continuous. The subordinate clause 'when the power went out' is correctly placed at the end.
- **Incorrect Answer (a)**: This incorrectly changes the tense to Simple Past.
- **Incorrect Answer (c)**: This incorrectly changes the tense to Present Perfect.
- **Incorrect Answer (d)**: This incorrectly changes the tense to Present Continuous.

**Rule**: For an interrogative sentence in the Simple Past with two objects (indirect 'him' and direct 'admission'), either can become the subject in the passive form. The structure is **Wh- word + was/were + object + V3?**

- **Correct Answer (d)**: Both (a) and (c) are correct passive transformations.
- In (a), the indirect object 'him' becomes the subject 'he'. The verb is 'was refused'.
- In (c), the direct object 'admission' becomes the subject. The verb is 'was refused', and the indirect object 'him' is preceded by 'to'.
- **Incorrect Answer (a)**: This is correct, but (c) is also correct.
- **Incorrect Answer (b)**: This incorrectly changes the tense to Simple Present.
- **Incorrect Answer (c)**: This is correct, but (a) is also correct.