Passage Summary: Scientists try to figure out why people are the way they are by asking them about their past, but because they have to rely on what people say, the studies aren't reliable.

Conclusion: Retrospective studies involving human subjects are unable to accurately identify the causes of those subjects' current traits.

Reasoning: These specific types of studies are forced to rely on the subjects' own personal accounts and memories of their pasts.

Analysis: The argument presents a premise about a method (relying on self-reports) and jumps to a conclusion about a result (unreliability). There is a clear gap here: why does relying on self-reports automatically make a study unreliable? To guarantee this conclusion, we need a bridge that says any study relying on subject reports is necessarily unreliable. Look for an answer that connects the 'reports' mentioned in the premise to the 'unreliability' mentioned in the conclusion.