When the water reached chest level and inched up worrisomely to the neckline, the passengers on the subway’s No. 5 line realized that these might be their last moments. One woman called her parents and gave them her bank account details; another was afraid to call her children, but uploaded a clip calling for help. All told, more than 500 people were trapped in this nightmarish scenario, which played out last month when torrential rains caused widespread flooding in the city of Zhengzhou in China. Water filled a subway tunnel and it took rescue crews four hours to get to the trapped passengers, 14 of whom didn’t survive.