The Internet will overtake radio in 2008 and become the world's fourth-largest advertising medium, a year earlier than forecast.        Global spending on Internet advertising increased from 18.7 billion U.S. dollars in 2005 to 24.9 billion dollars last year, according to Zenith Optimedia, the media-buying agency.        The Middle East and Asia are driving a boom in global advertising spending. Zenith predicted  _ of 7.7% in spending in Asia in the run-up to the 2008 Olympic Games in Beijing.       In the Middle East and Eastern Europe, advertising spending is growing faster than in North America and Western Europe, which are "maturing rapidly" as advertising markets, Zenith said.        Advertising spending in the Middle East increased by 22.4% between 2005 and 2006, compared with growth of 5.2% in America and 4 per cent in Western Europe. Zenith attributed the huge percentage share in the Middle East to the growth in local economies and high oil prices.  In addition to the Olympics, the U.S. presidential election and the European football championship in Austria and Switzerland next year will be the biggest contributors to overall growth during the next two years. However, Zenith noted, the market should brace itself for a fall in revenues after those big events end. Advertising spending in the Middle East increased greatly because of  _  .
the 2008 Olympic Games in Beijing the European football championship the growth in economies and high oil prices the U.S. presidential election