Passage Summary: You need good roads and bridges to live well, and building them makes life better. So, if a country is doing better, they definitely just spent a lot on roads and bridges.

Conclusion: If a nation's standard of living is rising, it must have invested heavily in its infrastructure.

Reasoning: Infrastructure is necessary for a high standard of living, and investing in it causes the standard of living to rise.

Analysis: The argument commits a classic 'Mistaken Reversal.' The author states that investment leads to a rise in living standards (Investment → Rise), but then concludes that a rise proves there was investment (Rise → Investment). This logic ignores the possibility that other factors—like a tech boom or a discovery of gold—could also cause a rise in the standard of living. Look for an answer that points out the argument's failure to consider alternative causes for the observed effect.