Change the following sentence into comparative degree.
Iron is the most useful of all metals.

The correct answer is Option A (Iron is more useful than any other metal.).

Key Points:
• The question tests changing a superlative degree sentence into a comparative degree sentence.
• The original sentence is in the superlative degree ('the most useful of all').
• To convert it into comparative without changing the meaning, we use 'more + adjective + than any other + singular noun'.
• So, 'Iron is more useful than any other metal' is the correct comparative form. Option 4 is the positive degree format.
• Key Takeaway: 'The most' (Superlative) changes to 'more ... than any other' in Comparative degree.