Transformation Rules (Degrees):
The sentence is in Superlative Degree ("the most useful").

Comparative: "Iron is more useful than any other metal." (Option A).
Positive: Uses the structure "as...as". When the Superlative is absolute (the best/the most), the Positive must start with "No other".

Option D ("Very few...") is used when the superlative is "one of the most" (e.g., "Iron is one of the most useful" $\rightarrow$ "Very few metals are as useful"). Since the original is absolute, Option B is correct.

Detailed Topic Insight (Degrees):
Adjectives change form to compare. 1. Positive: Describes one entity or equality (as tall as). 2. Comparative: Compares two entities (taller than). 3. Superlative: Compares three or more (the tallest). Note: Double comparatives (more better) are grammatical errors.

Sentence

Detailed Solution

Quiz360 Question Paper

Solution