**Rule**: When the active sentence uses structures like 'is to', 'am to', 'are to', 'was to', or 'were to' to indicate a plan or arrangement, the passive form is **Object + is/am/are/was/were to + be + V3**.

- **Correct Answer (a)**: The object 'my old car' becomes the subject. The structure 'was to be sold' is the correct passive form corresponding to the active 'was to sell'.
- **Incorrect Answer (b)**: 'had to be' implies obligation, which is a different meaning.
- **Incorrect Answer (c)**: 'was being sold' is the passive of the Past Continuous Tense.
- **Incorrect Answer (d)**: 'has to be' incorrectly changes the tense and meaning to present obligation.

**Rule**: For a Past Perfect Tense sentence, the passive voice structure is **Object + had + been + V3 + by + Subject**. Adverbs like 'already' are typically placed between the auxiliary verb 'had' and 'been'.

- **Correct Answer (c)**: The object 'him' becomes 'He'. The verb form 'had already been warned' correctly reflects the Past Perfect passive and the position of the adverb.
- **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)**: While grammatically understandable, placing 'already' after 'been' is less standard and can be awkward.

**Rule**: When the active sentence uses 'has to' or 'have to', the passive form is **Object + has/have to + be + V3**. The subordinate clause ('before I leave') remains unchanged.

- **Correct Answer (c)**: The object 'this task' becomes the subject. Since 'task' is singular, it takes 'has to be', followed by the past participle 'finished'. The rest of the sentence remains the same.
- **Incorrect Answer (a)**: 'has been finished' is the passive of the Present Perfect Tense, not of 'have to'.
- **Incorrect Answer (b)**: 'must' is a different modal, though similar in meaning.
- **Incorrect Answer (d)**: 'was to be' incorrectly changes the tense and meaning to a past plan.

**Rule**: When the active sentence uses 'has to'/'have to', the passive form is **Object + has/have to + be + V3**.

- **Correct Answer (c)**: The object 'this package' becomes the subject. Since 'package' is singular, it takes 'has to be', followed by the past participle 'sent'.
- **Incorrect Answer (a)**: 'is to be' implies a plan, which is different from the obligation of 'have to'.
- **Incorrect Answer (b)**: 'had to be' incorrectly changes the tense to the past.
- **Incorrect Answer (d)**: 'has been sent' is the passive of the Present Perfect Tense, not of 'have to'.

**Rule**: When a reporting verb (like believe, think, consider) is followed by an object and a to-infinitive, the passive structure is **New Subject (object from active) + is/was + V3 (of reporting verb) + to-infinitive**. The agent 'by them' is often omitted.

- **Correct Answer (a)**: The object 'him' becomes the subject 'He'. The verb 'believe' (Simple Present) becomes 'is believed'. The infinitive phrase 'to be innocent' remains unchanged. Omitting 'by them' is natural.
- **Incorrect Answer (b)**: This incorrectly changes the tense to Simple Past.
- **Incorrect Answer (c)**: This omits 'to be', which is grammatically incorrect in this structure.
- **Incorrect Answer (d)**: This is another possible passive form ('It is believed...'), but option (a) is the most direct transformation of the given sentence structure.

**Rule**: For an interrogative sentence in the Simple Present Tense starting with 'What', the passive structure is **What + is/am/are + V3 + by + subject?**

- **Correct Answer (a)**: The 'Wh-' word 'What' remains at the beginning and acts as the subject of the passive sentence. The verb 'is meant' is the correct singular passive form for the Simple Present Tense.
- **Incorrect Answer (b)**: This incorrectly changes the tense to Simple Past.
- **Incorrect Answer (c)**: This incorrectly changes the tense to Present Perfect.
- **Incorrect Answer (d)**: The word order is incorrect and awkward.

**Rule**: For an interrogative sentence with 'will have to' and a phrasal verb starting with 'Who', the passive structure is **By whom + will + object + have to be + V3 + preposition?**

- **Correct Answer (c)**: 'Who' becomes 'By whom'. The structure 'will...have to be paid for' is the correct passive form for the future necessity, retaining the preposition 'for'. The word order is correct for a question.
- **Incorrect Answer (a)**: This omits 'have to', changing the meaning.
- **Incorrect Answer (b)**: This is the passive of the Future Perfect Tense.
- **Incorrect Answer (d)**: 'would' is an incorrect modal change.

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

- **Correct Answer (d)**: The object 'widespread damage' becomes the subject. Since 'damage' is uncountable, the singular verb 'was' is used, followed by 'being' and the past participle 'caused'.
- **Incorrect Answer (a)**: This incorrectly changes the tense to Simple Past.
- **Incorrect Answer (b)**: This incorrectly changes the tense to Present Perfect.
- **Incorrect Answer (c)**: This incorrectly changes the tense to Present Continuous.

**Rule**: For a negative sentence in the Past Perfect Tense, the passive structure is **Object + had + not + been + V3 + by + Subject**.

- **Correct Answer (c)**: The object 'the book' becomes the subject. The verb form 'had not been finished' is the correct passive construction for a negative sentence in the Past Perfect 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)**: 'being' is incorrect; the past participle 'been' is required.

**Rule**: For a Simple Past Tense sentence with two objects (indirect 'me' and direct 'a job'), either can become the subject of the passive sentence.

- **Correct Answer (d)**: Both (a) and (b) are correct passive transformations.
- In (a), the direct object 'A job' becomes the subject. The passive verb is 'was offered', and the indirect object 'me' is preceded by 'to'.
- In (b), the indirect object 'me' becomes the subject 'I'. The passive verb is 'was offered', and the direct object 'a job' follows.
- **Incorrect Answer (a)**: This is correct, but (b) is also a valid transformation.
- **Incorrect Answer (b)**: This is correct, but (a) is also a valid transformation.
- **Incorrect Answer (c)**: This incorrectly changes the tense to Present Perfect.