题目

Metro Pocket Guide Metrorail(地铁) Each passenger needs a farecard to enter and go out.Up to two children under age five may travel free with a paying customer. Farecard machines are in every station.Bring small bills because there are no change machines in the stations and farecard machines only provide up to $5 in change. Get one day of unlimited Metrorail rides with a One Day Pass.Buy it from a farecard machine in Metro stations.Use it after 9:30 a.m.until closing on weekdays,and all day on weekends and holidays. Hours of service Open:5 a.m.Mon.—Fri.7 a.m.Sat.—Sun. Close:midnighHe made a serious mistake, but he took action to change that _________ it got worse.A. until B. when C. because D. before