**Rule**: To convert a Future Simple Tense sentence to passive voice, the structure is **Object + will/shall + be + V3 + by + Subject**. - **Correct Answer (a)**: The object 'his new book' becomes the subject. The passive verb form 'will be released' correctly reflects the Future Simple Tense. - **Incorrect Answer (b)**: 'would' is an incorrect modal verb, changing the certainty of the statement. - **Incorrect Answer (c)**: This incorrectly changes the tense to Present Continuous. - **Incorrect Answer (d)**: This incorrectly changes the tense to Future Perfect.

**Rule**: In a complex sentence, the main clause 'They were not serving dinner' (negative Past Continuous) is passivized, while the subordinate clause 'when we arrived' remains unchanged. - **Correct Answer (a)**: The object 'dinner' becomes the subject. The verb form 'was not being served' is the correct passive for the negative Past Continuous. The agent 'by them' is omitted. - **Incorrect Answer (b)**: This incorrectly changes the tense to Present Perfect. - **Incorrect Answer (c)**: This incorrectly changes the tense to Simple Past. - **Incorrect Answer (d)**: This incorrectly changes the tense to Present Continuous.

**Rule**: When the active sentence uses 'had to' to show past necessity, the passive form is **Object + had to + be + V3**. - **Correct Answer (d)**: The object 'the trip' becomes the subject. The structure 'had to be postponed' is the correct passive form for the past necessity. - **Incorrect Answer (a)**: 'had been postponed' is the passive of the Past Perfect Tense ('had postponed'), not 'had to postpone'. - **Incorrect Answer (b)**: 'has to be' incorrectly changes the tense to the present. - **Incorrect Answer (c)**: 'was to be' implies a past plan, which is a different meaning from past necessity.

**Rule**: For a negative sentence in the Past Perfect Tense, the passive structure is **Object + had + not + been + V3 + by + Subject**. Adverbs like 'yet' are usually placed after 'not'. - **Correct Answer (a)**: The object 'the results' becomes the subject. The verb form 'had not yet been announced' is the correct passive construction and adverb placement. - **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 'yet not' is grammatically incorrect.

**Rule**: For an interrogative sentence with a past modal (modal + have + V3) starting with 'Who', the passive structure is **By whom + modal + have been + V3?** - **Correct Answer (b)**: 'Who' becomes 'By whom'. The past modal passive form 'could have been done' is used. The word order is correct for a question, with the modal 'could' coming before the subject 'this'. - **Incorrect Answer (a)**: 'could this be done' is the passive for a present modal ('could do'), not a past modal. - **Incorrect Answer (c)**: This has incorrect word order for a question; 'could' should be before 'this'. - **Incorrect Answer (d)**: This also has incorrect word order; the subject 'this' should come between 'could' and 'have'.

**Rule**: For active sentences using the 'be going to' future form, the passive structure is **Object + is/am/are + going to be + V3**. - **Correct Answer (d)**: The object 'a new park' becomes the subject. The structure 'is going to be built' is the correct passive conversion. - **Incorrect Answer (a)**: This is the passive of the Present Continuous tense ('is building'). - **Incorrect Answer (b)**: This changes the structure to the 'will' future. - **Incorrect Answer (c)**: This incorrectly changes the tense to Present Perfect.

**Rule**: When the active sentence uses 'had to' to show past necessity, the passive form is **Object + had to + be + V3**. The agent 'by them' can be omitted. - **Correct Answer (c)**: The object 'the meeting' becomes the subject. The structure 'had to be cancelled' is the correct passive form for the past necessity. The agent 'by them' is correctly and naturally omitted. - **Incorrect Answer (a)**: 'had been cancelled' is the passive of the Past Perfect Tense ('had cancelled'), not 'had to cancel'. - **Incorrect Answer (b)**: 'was to be' implies a past plan, which is a different meaning from past necessity. - **Incorrect Answer (d)**: 'has to be' incorrectly changes the tense to the present.

**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 'had' and 'been'. - **Correct Answer (d)**: The object 'the topic' becomes the subject. The verb form 'had already been explained' is the correct passive construction. - **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 Simple Present.

**Rule**: For an interrogative sentence with a past modal starting with 'Who', the passive structure is **By whom + modal + have been + V3?** - **Correct Answer (c)**: 'Who' becomes 'By whom'. The past modal passive form 'could have been written' is used. The word order is correct for a question, with the modal 'could' coming before the subject. - **Incorrect Answer (a)**: 'could be written' is the passive for a present modal. - **Incorrect Answer (b)**: The word order is incorrect; the subject 'such a beautiful poem' should come between 'could' and 'have'. - **Incorrect Answer (d)**: 'can' is a different modal.

**Rule**: For an interrogative sentence in the Simple Past Tense starting with a 'Wh-' word, the passive structure is **Wh- word + was/were + object + V3 + by + subject?** - **Correct Answer (d)**: The 'Wh-' word 'How' remains at the beginning. The object 'the solution' is singular, so 'was' is used, followed by the past participle 'found'. - **Incorrect Answer (a)**: This incorrectly changes the tense to Present Perfect. - **Incorrect Answer (b)**: This incorrectly changes the tense to Simple Present. - **Incorrect Answer (c)**: This incorrectly changes the tense to Past Continuous.