There seems to be some confusion with the given question as it is not clear what the options 'a', 'b', 'c', and 'd' represent. Without further context or information, it is difficult to provide a specific explanation for why option 'D' is considered the correct answer.

However, I can provide some general guidance on how to approach multiple-choice questions.

1. Read the question carefully: Before looking at the options, make sure you understand what the question is asking. Pay attention to any specific details or keywords that may guide your answer.

2. Analyze each option: Once you understand the question, carefully examine each option provided. Look for any clues or information that can help you determine the correct answer.

3. Elimination strategy: If you are unsure about the correct answer, try using an elimination strategy. Cross out any options that you know are incorrect, which will narrow down your choices and increase your chances of selecting the correct answer.

4. Consider all possibilities: Sometimes, multiple options may seem plausible. In such cases, try to consider all possibilities and think critically about the question. Look for any clues or hints within the question that may guide you towards the correct answer.

5. Use prior knowledge: If the question is related to a specific topic or subject, try to recall any relevant information or concepts you have learned previously. This can help you make an informed decision and select the correct answer.

In conclusion, without more information or context, it is not possible to explain why option 'D' is considered the correct answer. However, by following the steps outlined above, you can improve your chances of selecting the correct option in multiple-choice questions.