Flex 4 <mx:Component> could not resolve

I am using flash builder 4 to run sample application from "Getting Started with FLEX 3", but the code can't run because there is one pl开发者_如何学Pythonace that FB4 can't resolve, I guess this is because the library has been obsolete but after a tons of search I can't find the solution.

Thanks. Bin

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With Flex4 you'll want fx:Component instead