资料：Are walkers smarter than drivers?

A report published last month says metropolitan areas in the United States that were found to be more pedestrian-friendly also often had higher levels of GDP -and their citizens were better educated.

The study was conducted by Smart Growth America, an urban advocacy group based in the District of Columbia. It looked at the 30 biggest metro zones in the US, and ranked them by how much office, retail, and residential area was conducive to walking.

The question is, why? Do brainier people just like to walk and not drive? It's a complicated answer. What we don't know is whether walkable places attract educated people, or whether educated people move to certain places that then become more walkable.

That's not all: Education levels aren't just higher in walkable cities. GDP is, too. The gap between the highest and lowest urban metros by GDP in the study is a chasm of 49%, which scholar calls a "first and second world gap. This is serious stuff."

Of course, correlation doesn't equal causation. There's not enough data to definitively say why these urban areas are filled with educated people. But it's definitely a starting point for conversation: Many socioeconomic and generational trends the world over could help explain why university graduates gravitate toward crowded, subway-lined metropolises these days. In fact, such an intellectual influx has started to change the entire faces of some urban areas.

Increased urbanization isn't the only reason car-eschewing cities see smarter citizens. Young people play a role, too. Millennials-those born between around 1981 and 1996-are the most educated generation in history. Nearly half of them hold a bachelor's degree or higher. They're also all moving to cities, unlike their parents. These spikes in the workforce translate into metros with higher GDP and higher overall education levels.

What can be the possible explanation according to the study?

• A.Urbanization
• B.Young people
• C.Both
• D.Unknown