Passage Summary: We knew one of two things caused a crash: a bad lane change or speeding. We proved the bad lane change happened, so we're concluding the speeder isn't at fault.

Conclusion: The driver of the second vehicle cannot be held responsible for the accident.

Reasoning: The accident was caused by either the first driver's failure to signal or the second driver's speeding; since it is confirmed the first driver did not signal, the second driver is cleared.

Analysis: The argument relies on a 'one or the other' framework, assuming that if one cause is proven, the other must be excluded. To evaluate this, we need to know if both factors could have contributed simultaneously. If the second driver was speeding *and* the first driver didn't signal, both could potentially be liable. Look for an answer choice that addresses whether these two causes are mutually exclusive or if they could both be true.