Workers prepare for the trial operation of the first subway line in Southwest 皇冠体育app's mountainous metropolis of Chongqing, July 28, 2011. The 15.7 km long subway line has a total of 13 stations and is the first of its kind built in a mountainous place. [Photo/CFP]

Local residents wait inside a subway station before getting onboard the train to experience the trial operation of the first subway line in Southwest 皇冠体育app's mountainous metropolis of Chongqing, July 28, 2011. [Photo/CFP]