Passage Summary: After a big quake in California, local students started dreaming about it, but students in Canada didn't, leading researchers to conclude the experience caused the dreams.

Conclusion: Experiencing an earthquake is the direct cause of people having dreams about earthquakes.

Reasoning: Students who lived through a California earthquake reported such dreams, while a control group in Ontario who did not experience the quake had almost no earthquake dreams.

Analysis: This is a classic causal argument based on a comparison between two groups, but it has a significant chronological gap. To strengthen this claim, we need to ensure that the 'cause' (the earthquake) actually led to a change in the 'effect' (the dreams). Look for an answer that establishes a baseline, such as evidence that the California students weren't already dreaming about earthquakes before the event happened. By ruling out the possibility that these students were predisposed to such dreams regardless of the quake, the causal link becomes much more robust.