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He called on more celebrities and people to join the public and promotional events of the Shanghai Expo.
Yao presented a proposal called "contribute to Green Expo, share a bright future" at the ceremony.
"I hope more people especially the teenagers will join us to popularize Shanghai Expo and disseminate its ideas of green, health and affection," he said.
Apart from Yao, international movie star Jackie Chan and well-known pianist Lang Lang are also the ambassadors of Shanghai Expo who launched the event.
The public welfare activity, held by the China Council for the Promotion of International Trade, China Ministry of Culture and Coordination Bureau of Shanghai Expo Affairs, features various activities such as charitable parties and public speeches. Some children from the disaster and depressed areas will get sponsors' financial aid to take part in the Shanghai Expo.
Shanghai Expo 2010 will start on May 1 and end on Oct 31. It is estimated that more than 70 million visitors will arrive in Shanghai.