Explanation:

This question requires us to select the correct tense form to complete a sentence that describes a sequence of past events. The sentence structure 'When we ..., we went for a walk' indicates that one action happened before another in the past. This is a classic scenario for using the Past Perfect tense. **Understanding the Context:** The sentence presents two actions: 'having dinner' and 'going for a walk'. The phrase 'we went for a walk' is in the simple past tense, indicating a completed action in the past. The first clause, 'When we ... our dinner', describes an action that was completed *before* the action of going for a walk. When one past action precedes another past action, the earlier action is typically expressed using the Past Perfect tense. **The Past Perfect Tense:** The structure of the Past Perfect tense is 'had + past participle (V3)'. The verb 'to have' can be used in various senses, including 'to eat' or 'to finish'. In this context, 'had our dinner' means 'finished eating our dinner'. The past participle of the verb 'to have' is 'had'. Let's evaluate each option: **Option (A): had having** This option is grammatically incorrect. 'Had' is the auxiliary verb for the past perfect, and it must be followed by a past participle. 'Having' is a present participle or a gerund, not a past participle. Therefore, 'had having' is an invalid tense construction. **Option (B): had had** This option is grammatically correct and fits the context perfectly. The first 'had' is the auxiliary verb for the Past Perfect tense. The second 'had' is the past participle of the main verb 'to have' (meaning 'to consume' or 'to finish'). So, 'When we had had our dinner' correctly conveys that the action of finishing dinner was completed before we went for a walk. This construction precisely expresses the sequence of past events. **Option (C): had have** This option is grammatically incorrect. Similar to option (A), 'had' must be followed by a past participle. 'Have' is the base form of the verb, not its past participle. Therefore, 'had have' is an invalid tense construction. **Option (D): have had** This option represents the Present Perfect tense ('have/has + past participle'). The Present Perfect is used for actions that started in the past and continue to the present, or actions completed in the past with a result relevant to the present. However, the second clause 'we went for a walk' is in the simple past, indicating a completed action in the past. Using 'have had' would create a mismatch in tenses and an illogical sequence of events, as it would imply the dinner was just finished or has present relevance, which doesn't fit the subsequent simple past action. The Past Perfect is required to clearly establish the earlier completion of dinner relative to the walk. **Conclusion:** To correctly express that the dinner was completed *before* the walk, the Past Perfect tense is necessary. The correct form for the Past Perfect of 'to have' (meaning to eat/finish) is 'had had'. Therefore, option (B) is the correct answer.