y = 0;
ad = new Array(y);
ad[y++] = '<a href="http://www.fundacion.telefonica.com/vida" target="new"><img src="http://w3art.es/ads/168x120vida_2010.gif" border="0"></a>'
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ad[y++] = '<a href="http://www.fundacion.telefonica.com/arteytecnologia/exposiciones/lab_granvia.htm" target="new"><img src="http://w3art.es/ads/168x120_telefonica2010.gif" border="0"></a>'
x = Math.floor(Math.random()*(y));
document.write(ad[x]);