The question tests the understanding of synonymous expressions. The correct answer is A. 'proved to be' carries a similar meaning to 'turned out to be', indicating a result or outcome that has been confirmed. Option B, 'seemed to be', suggests an appearance or impression that might not be true. Option C, 'appeared to be', is similar to B, suggesting a visual impression. Option D, 'was expected to be', indicates an expectation rather than an actual outcome. The core concept here is the use of synonymous verbs to express confirmation of a fact or result.