By Brian Dumaine, assistant managing editor
Quick: which nation builds the most wind turbines? If you guessed America, with its blustery Great Plains dotted with whirring GE blades, you'd be wrong. In 2009, China became the planet's largest producer. What's going on here? While America was digging itself out of its financial crisis, China quietly positioned itself to become a leader in what promises to be the largest emerging industry of the 21st century: green tech.