The correct option for the sentence "Olukayode .... as a mechanic when he was young, but now he is a driver" is B. used to work. Step-by-Step Explanation:

1. Understanding the Context: The sentence discusses Olukayode's past occupation as a mechanic and contrasts it with his current job as a driver. This indicates that he no longer works as a mechanic, which is a key point in determining the correct phrase to fill in the blank.
2. Analyzing the Options:
3. A. had been working: This phrase suggests a continuous action in the past that was completed before another past action. It implies that he was working as a mechanic for a period of time, but it does not convey the idea of a habitual action or a past state that has changed. Therefore, it does not fit well in this context.
4. B. used to work: This phrase is specifically used to describe a past habit or a state that was true in the past but is no longer the case. It perfectly fits the context of the sentence, indicating that Olukayode regularly worked as a mechanic when he was young, but he has since changed his occupation to a driver. This option captures the essence of a past routine that has now changed.
5. C. would work: This phrase is often used to describe a future action that is dependent on a condition or a habitual action in the past that is not as strong as "used to." It does not convey the same sense of a past state that has changed, making it less suitable for this sentence.
6. D. would have worked: This phrase is used to describe a hypothetical situation in the past that did not occur. It implies that there was a possibility of working as a mechanic, but it did not happen. This does not fit the context of Olukayode's actual past experience as a mechanic.
7. Conclusion: Given the context of the sentence, "used to work" is the most appropriate choice because it clearly indicates that Olukayode had a regular job as a mechanic in the past, which he no longer holds.

Summary of Why Option B is Correct:

• "Used to work" indicates a past habit or state that has changed, which fits the context of the sentence.
• It clearly communicates that Olukayode was a mechanic in the past but is now a driver.

Revision Summary:

• "Used to" is used for past habits or states that no longer exist.
• "Had been working" suggests a continuous action that is not suitable for this context.
• "Would work" implies a conditional or habitual action but lacks the clarity of a past state.
• "Would have worked" refers to a hypothetical situation that did not occur, making it irrelevant here.

By understanding these distinctions, you can better choose the correct phrases in similar contexts in the future.