As we enter the 21st century, a new global economy draws nations ever closer. But our growing interdependence 【21】______ on much more than technology and trade. For we are linked intrinsically by the physical and biological webs that 【22】______ life on our planet -- and, increasingly, by the threat of their unraveling. Indeed, 【23】______ we reach across borders and face this threat together, the next century may 【24】______ an Earth in ecological crisis, with half of all 【25】______ gone, and our grandchildren enduring deadly floods, drought and disease 【26】______ by global warming.
When millions across America 【27】______ the first Earth Day 30 years ago, our focus understandably was our own backyard. Our rivers were 【28】______ on fire, and our skylines were disappearing behind a 【29】______ of smog. American's remarkable environmental progress in the years 【30】______ is powerful testament to our national will, our technological prowess and our 【31】______ in a better future. Protecting the environment is today a bedrock American value, 【32】______ important to us as safe neighborhoods and good schools. What's more, three decades of experience have 【33】______ the naysayers wrong. Tending to the environment has not 【34】______ our economy. 【35】______ , our air and water are the cleanest they have been in a generation, even as we enjoy the longest economic 【36】______ in our nation's history.
America's responsibility now, as we mark the first Earth Day of a new millennium, is to bring these lessons to bear against new, more 【37】______ environmental challenges. We must look well 【38】______ our own cities and countryside, make environment a core foreign policy 【39】______ and provide the leadership needed to put all nations on a cleaner, more sustainable path to 【40】______ .
【21】

A. hinges
B. decides
C. lives
D. revolves