Iron is one the most useful metals. (Make it Positive) ?

The question asks us to transform a negative structure into a positive one, focusing on the utility of iron as a metal. The statement to be rephrased is "Iron is one of the most useful metals," which highlights its significance among other metals.

Option A, "Iron is a useful metal," effectively simplifies and positively states the original assertion. It maintains the emphasis on iron’s utility while removing the unnecessary comparative aspect present in the original statement. This creates a clear and positive affirmation about iron.

Option B, "Very few metals are so useful metals as iron," uses a comparative structure that implies a certain degree of negativity by suggesting that iron is exceptionally useful but hints that others are less so. This could be interpreted as implied limitation rather than outright positivity.

Option C, "Iron is a more useful metal," introduces a comparative aspect that ironically shifts focus to a ranking rather than simply acknowledging its usefulness.

Option D, "Iron is more useful metals," is grammatically incorrect, as 'more' is not appropriately applied to a singular noun like 'metal.'

In summary, Option A serves as the clearest, most unequivocal positive assertion about the practicality of iron, making it the correct choice.