In systems using adversarial processes, an attorney may impeach an opposing party ' s witness...

The correct answer is C. The CFE Manual explains that in adversarial systems, one of the most common methods of impeachment is to show that the witness made prior inconsistent statements. Impeachment is used to attack a witness’s credibility, reliability, or truthfulness. If a witness previously said something materially different from what the witness now says at trial, opposing counsel can use that inconsistency to suggest that the testimony is unreliable or false.

The other options do not describe impeachment. Option A, testifying from personal knowledge, generally supports credibility rather than undermines it. Option B, having a reputation for truthfulness, also strengthens credibility and is the opposite of impeachment. Option D, possessing a strong ability to observe, similarly suggests reliability rather than weakness. The Manual lists several common impeachment methods, including showing bias, impaired ability to observe, felony convictions, a reputation for untruthfulness, and prior inconsistent statements. Among the choices provided, only C matches one of those recognized impeachment techniques. Therefore, in an adversarial process, an attorney may impeach an opposing witness by proving that the witness previously made inconsistent statements, making C the correct answer.