Tourists visit the park of the International Horticultural Exposition 2011 on battery vehicles in Xi'an, capital of northwest China's Shaanxi Province, April 28, 2011. The International Horticultural Exposition 2011 kicked off here Thursday. (Xinhua/Jiao Weiping)

Tourists visit the park of the International Horticultural Exposition 2011 in Xi'an, capital of northwest China's Shaanxi Province, April 28, 2011. The International Horticultural Exposition 2011 kicked off here Thursday. (Xinhua/Jiao Weiping)

A volunteer sits beside the bicycles offered for tourists at the park of the International Horticultural Exposition 2011 in Xi'an, capital of northwest China's Shaanxi Province, April 28, 2011. The International Horticultural Exposition 2011 kicked off here Thursday. (Xinhua/Jiao Weiping)

Tourists visit the park of the International Horticultural Exposition 2011 in Xi'an, capital of northwest China's Shaanxi Province, April 28, 2011. The International Horticultural Exposition 2011 kicked off here Thursday. (Xinhua/Jiao Weiping)

Tourists enter the park of the International Horticultural Exposition 2011 in Xi'an, capital of northwest China's Shaanxi Province, April 28, 2011. The International Horticultural Exposition 2011 kicked off here Thursday. (Xinhua/Xu Zijian)