Option (A) is correct because the textbook context clearly states that 'the constitution has to be able to respond to the challenges that may arise in the future' and 'Whenever society would veer toward any particular opinion, a change in the constitutional provisions would be required.' This directly supports the idea that circumstances change and require suitable changes in the constitution. The makers of the Constitution recognized that the document 'may require modifications' and that it is 'not a static document' but one that must respond to changing circumstances.

Option (B), while partially valid, is more of a consequence rather than the fundamental reason. Options (C) and (D) are incorrect. The context emphasizes that the constitution has 'something that has a more durable importance' and some provisions are 'so central to the spirit of the Constitution that the Constitution makers were anxious to protect these from change,' contradicting option (C). Regarding option (D), the context states 'The Constitution is a statement of the philosophy of the country' — not the philosophy of the existing government.