**Rule**: The **Simple Past Tense** (negative form) is used to talk about a state that was true up to a certain point in the past. **Correct Usage**: 'didn't learn' correctly describes the lack of ability during the period before the speaker was 12. **Incorrect Options**: (b) 'wasn't learning' refers to an ongoing process. (c) 'hadn't learned' could also be used, but simple past is more common and direct for this type of statement. (d) 'don't learn' is a present tense.

**Rule**: The **Simple Past Tense** is used for a short, completed past action which is then contrasted with another action. **Correct Usage**: 'rang' is the single, completed event. The second clause describes his reaction (or lack thereof). Simple Past is clear and effective. **Incorrect Options**: (b) 'was ringing' suggests it was continuous. (c) 'had rung' would imply it rang before another past event. (d) 'rings' is a present tense.

**Rule**: The **Simple Past Tense** is used for a completed past action, often followed by the result of that action. **Correct Usage**: 'called' is the simple action he took, and 'went' is the immediate result. Both are in the Simple Past. **Incorrect Options**: (b) 'was calling' is an ongoing action. (c) 'had called' would need another past reference. (d) 'calls' is a present tense.

**Rule**: The **Past Perfect Continuous Tense** is used to emphasize the duration of a long journey or activity that happened before a concluding past event. **Correct Usage**: 'had been traveling' emphasizes the long, continuous journey ('for weeks') that preceded the final discovery ('discovered'). **Incorrect Options**: (a) 'traveled' is less descriptive. (b) 'were traveling' is the wrong sequence. (d) 'had traveled' (Past Perfect) focuses on the completion of the travel, not the process.

**Rule**: The **Simple Past Tense** is used for a completed action that took place in a specific, finished historical period. **Correct Usage**: 'in the 16th century' specifies a definite past time, requiring the Simple Past verb 'painted'. **Incorrect Options**: (b) 'was painting' describes the process. (c) 'had painted' would need a later past reference. (d) 'has painted' is a present tense.

**Rule**: The **Simple Past Tense** (negative) is used for a past inaction that caused a subsequent past feeling. **Correct Usage**: I 'was' disappointed (past state) because he 'didn't keep' his promise (the reason, a past inaction). 'hadn't kept' is also correct. **Incorrect Options**: (b) 'wasn't keeping' is incorrect. (c) 'hadn't kept' (Past Perfect) is also a strong correct answer, emphasizing the prior failure. (d) 'doesn't keep' is a present tense.

**Rule**: The **Simple Past Passive** (was/were + past participle) is used for a completed action in the past at a specific time, where the subject is the receiver of the action. **Correct Usage**: The castle is the receiver of the building action. 'was built' is the correct passive form for this completed historical event. **Incorrect Options**: (b) 'had been built' would be used if it was built before another past event. (c) 'built' is active voice. (d) 'builds' is a present tense.

**Rule**: The **Past Perfect Tense** is used for a past action that began before another past action. The adverb 'already' reinforces this. **Correct Usage**: The film's start ('had already started') happened before our arrival ('got to the cinema'). **Incorrect Options**: (a) 'already started' (Simple Past) is common in informal speech but Past Perfect is more grammatically precise. (c) 'was already starting' implies it started at the same moment. (d) 'already starts' is a present tense.

**Rule**: The **Past Continuous Tense** is used to describe a process that was happening at the same time as another event. **Correct Usage**: The process of the sun going down ('was setting') was happening simultaneously with the sky changing color ('turned'). It describes a gradual scene. **Incorrect Options**: (a) 'set' (Simple Past) is also possible. (c) 'had set' would mean the sun was already down. (d) 'sets' is a present tense.

**Rule**: The **Simple Past Tense** is used for a single, completed event at a specific time in the past. **Correct Usage**: 'a decade ago' is a definite past time, so 'collapsed' is the correct verb for this finished event. **Incorrect Options**: (a) 'was collapsing' is a process. (b) 'had collapsed' would need another past reference. (d) 'collapses' is a present tense.