We already know that the average hourly wage decreased last year and the fact that it decreased over the last three years is not relevant. Instead, we need to know how it increased in each region of the country last year, even though it decreased in the country as a whole.

This helps to explain the paradox. As many jobs moved from higher-paying to lower-paying regions, those jobs were paid less, decreasing the average hourly wage nationally, but increasing it in each region.

We don’t know how the country’s unemployment rate might affect its average hourly wage. Regardless of unemployment, we know that the average hourly wage increased in each region but decreased nationwide, and we need an answer that helps to explain this paradox.

Regardless of its rate of increase, we know that the average hourly wage for full-time jobs increased in each region. (D) doesn’t help to explain how the average hourly wage decreased nationwide, given the fact that it increased in each region.

We’re only concerned about the change in the average hourly wage for full-time jobs overall. It doesn't matter which jobs saw pay increases or decreases, just that the average hourly wage rose in each region but fell nationwide.