**Rule**: For a sentence in the Simple Past Tense, the passive voice structure is **Object + was/were + V3 + by + Subject**. - **Correct Answer (a)**: The object 'the child' becomes the subject. Since 'child' is singular, 'was' is used, followed by the past participle 'frightened'. - **Incorrect Answer (b)**: 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 a negative sentence in the Past Perfect Tense, the passive structure is **Object + had + not + been + V3 + by + Subject**. - **Correct Answer (a)**: The object 'the crisis' becomes the subject. The verb form 'had not been foreseen' is the correct passive construction for a negative sentence in the Past Perfect 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)**: This incorrectly changes the tense to Past Continuous.

**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 predicted' is used. The word order is correct for a question, with the modal 'could' coming before the subject 'such a result'. - **Incorrect Answer (a)**: 'could be predicted' is the passive for a present modal. - **Incorrect Answer (b)**: 'can' is a different modal. - **Incorrect Answer (d)**: This has incorrect word order for a question.

**Rule**: The Present Continuous Tense can be used for a fixed plan in the near future. Its passive form is **Object + is/am/are + being + V3**. The future time adverbial ('next year') is retained. - **Correct Answer (a)**: The object 'a new product' becomes the subject. The passive verb 'is being launched' correctly reflects the Present Continuous used for a future plan. - **Incorrect Answer (b)**: While 'will be launched' is also correct for the future, option (a) is the direct passive conversion of the given Present Continuous tense. - **Incorrect Answer (c)**: This incorrectly uses the Simple Present passive, which is not appropriate for a future plan. - **Incorrect Answer (d)**: This incorrectly changes the tense to Present Perfect.

**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.