Choose the correct order in the proof of √2.

Correct answer: Rational assumption → a² = 2b² → a even → b even → contradiction

The correct answer is A because it follows the contradiction proof in the required logical order. Assume √2 is rational and write it as a/b in lowest terms, where a and b are coprime integers and b is nonzero. Squaring gives a²/b² = 2, hence a² = 2b². Therefore a² is even, so a is even; write a = 2k. Substitution gives 4k² = 2b², or b² = 2k², so b is also even. Thus both a and b have a common factor 2, contradicting the assumption that the fraction was in lowest terms. The other sequences omit the essential algebra or replace proof with an unsupported decimal guess.