• http://www.areatecnologia.com/estructuras.htm

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• http://mariademolina.blogspot.com.co/2013/02/estructuras-animaciones.html

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• https://www.youtube.com/watch?v=9UIv1aWDh5E

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• https://www.youtube.com/watch?v=6gwhD8POBt4

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• https://www.youtube.com/watch?v=5gw31zZUeQo

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