单选题：Questionsare based on the following passage.It is easy to m

Questionsare based on the following passage.
It is easy to miss amid the day-to-day headlines of global economic recession, but there is a less conspicuous kind of social upheaval (剧变) underway that is fast altering both the face of the planet and the way human beings live. That change is the rapid acceleration of urbanization. In 2008, for the first time in human history, more than half the world's population was living in towns and cities. And as a recently published paper shows, the process of urbanization will only accelerate in the decades to come--with an enormous impact on biodiversity and potentially on climate change.
As Karen Seto, the lead author of the paper, points out, the wave of urbanization isn't just about the migration of people into urban environments, but about the environments themselves becoming bigger to accommodate all those people. The rapid expansion of urban areas will have a huge impact on biodiversity hotspots and on carbon emissions in those urban areas.
Humans are the ultimate invasive species--when. they move into new territory, they often displace the wildlife that was already living there. And as land is cleared for those new cities--especially in the densetropical forests--carbon will be released into the atmosphere as well. It's true that as people in developing nations move from the countryside to the city, the shift may reduce the pressure on land, which could in turn be good for the environment. This is especially so in desperately poor countries, where residents in the countryside slash and burn forests each growing season to clear space for farming. But the real difference is that in developing nations, the move from rural areas to cities often leads to an accompanying increase in income--and that increase leads to an increase in the consumption of food and energy, which in turn causes a rise in carbon emissions. Getting enough to eat and enjoying the safety and comfort of
living fully on the grid is certainly a good thing--but it does carry an environmental price.
The urbanization wave can't be stopped--and it shouldn't be. But Seto's paper does underscore the importance of managing that transition. If we do it the right way, we can reduce urbanization's impact on the environment. "There's an enormous opportunity here, and a lot of pressure and responsibility to think about how we urbanize," says Seto. "One thing that's clear is that we can't build cities the way we have over the last couple of hundred years. The scale of this transition won't allow that." We're headed towards an urban planet no matter what, but whether it becomes heaven or hell is up to us.
What issue does the author try to draw people's attention to? A．The shrinking biodiversity worldwide.
B．The rapid increase of world population.
C．The ongoing global economic recession.
D．The impact of accelerating urbanization.