People visit the International Conference and Exhibition on Liquefied Natural Gas (LNG) in Houston, the United States, April 17, 2013. The 17th LNG International Conference and Exhibition, one of the world's largest LNG events, opened in Houston on Tuesday. The event, which debuted in 1968, is held once every three years, alternating between producing and consuming countries and regions. (Xinhua/Zhang Yongxing)