Passage Summary: If it had been freezing, my plants would be dead and wouldn't be blooming; since they are blooming, it clearly didn't freeze.

Conclusion: The temperature did not drop below freezing during the previous week.

Reasoning: If it had frozen, the flowers would have died; if the flowers had died, they would not be blooming; but the flowers are currently blooming.

Analysis: The logic here is a perfect conditional chain: A implies B, and B implies C. The author then observes that C is false (Not C), which allows them to conclude that A must also be false (Not A). This is a valid use of the contrapositive across a transitive link. To find the parallel, look for an answer that sets up two 'if-then' statements and then denies the final result to disprove the initial condition.