**Rule**: The **Past Continuous Tense** is used to describe two or more actions that were happening simultaneously in the past. **Correct Usage**: The children's building ('were building') and the parents' relaxing ('were relaxing') were two parallel, ongoing activities. **Incorrect Options**: (a) 'built' (Simple Past) suggests a completed action. (c) 'had built' and (d) 'had been building' imply the building happened before the relaxing.

**Rule**: The **Past Continuous Tense** is used to ask about an activity that was in progress at a specific time in the past. **Correct Usage**: The question asks about the ongoing action at the precise moment of '10 PM last Saturday'. 'were you doing' is the correct structure for this inquiry. **Incorrect Options**: (a) 'did, do' (Simple Past) would ask what you did in general on Saturday, not at that specific time. (c) 'had, done' and (d) 'had you been doing' would require another past event as a reference point.

**Rule**: The **Past Perfect Continuous Tense** (had been + verb-ing) is used to emphasize the duration of a continuous action that was happening before another past action occurred. **Correct Usage**: 'had been working' emphasizes the long ten-year period of employment that occurred before the past action of his 'decided' to leave. **Incorrect Options**: (a) 'worked' (Simple Past) doesn't emphasize the duration as effectively. (b) 'was working' (Past Continuous) doesn't fit the sequence of events. (d) 'has worked' is a present tense.

**Rule**: The **Simple Past Tense** is used for a short, immediate reaction to another past event. **Correct Usage**: The soldiers 'cheered' as a spontaneous and completed reaction to the announcement ('was announced'). **Incorrect Options**: (b) 'were cheering' suggests they were already cheering before the announcement. (c) 'had cheered' is the wrong sequence. (d) 'cheer' is a present tense.

**Rule**: The **Past Perfect Continuous Tense** is used to emphasize the duration of a continuous state or action that was happening before another past event took place. **Correct Usage**: 'had been suffering' emphasizes the long, continuous period of suffering ('for several hours') that occurred before the doctor's arrival. **Incorrect Options**: (a) 'suffered' (Simple Past) lacks emphasis on duration. (b) 'was suffering' (Past Continuous) doesn't connect to the subsequent event as clearly. (d) 'had suffered' (Past Perfect) focuses on the completion of suffering, which is unlikely.

**Rule**: The **Past Perfect Continuous Tense** is used to emphasize the duration of an activity that was in progress before another past event occurred. **Correct Usage**: 'had been cleaning' emphasizes the long period of cleaning ('for hours') that took place before the guests 'arrived'. **Incorrect Options**: (a) 'cleaned' (Simple Past) is the wrong sequence. (b) 'were cleaning' suggests they were still cleaning when the guests arrived. (d) 'had cleaned' (Past Perfect) focuses on the completion of the cleaning, not the duration.

**Rule**: The **Simple Past Tense** is used to narrate a completed action in the past. **Correct Usage**: 'told' is the correct verb to describe the single, completed act of storytelling. **Incorrect Options**: (b) 'was telling' would describe the story in progress. (c) 'had told' would be used if another action followed. (d) 'tells' is a present tense.

**Rule**: The **Past Perfect Tense** is used for a past action that was fully completed before another past event began. **Correct Usage**: The preparation of the kitchen ('had prepared') was finished before the arrival of the first customers ('arrived'). **Incorrect Options**: (a) 'prepared' (Simple Past) is less precise. (b) 'was preparing' suggests he was still preparing when they arrived. (d) 'prepares' is a present tense.

**Rule**: The **Past Perfect Tense** (had + past participle) is used for a past action that happened before another past action. **Correct Usage**: The suspect's action of lying ('had lied') happened before the detective's realization ('realized'). The Past Perfect clearly shows this sequence. **Incorrect Options**: (a) 'lied' (Simple Past) is possible, but less precise about the timeline. (b) 'was lying' (Past Continuous) would imply he was in the act of lying when the detective realized. (d) 'has lied' is a present tense.

**Rule**: The **Past Perfect Continuous Tense** is used to describe a long, continuous action that caused a subsequent past state. **Correct Usage**: The children 'were' covered in mud (past state) because they 'had been playing' (long, prior continuous action) for a long time. **Incorrect Options**: (a) 'played' is less descriptive. (b) 'were playing' would be simultaneous. (c) 'had played' (Past Perfect) focuses on completion.