跟美国学的

Protests lead to temporary closings of Bay Area train stations
By the CNN Wire Staff
August 22, 2011 9:50 p.m. EDT

(CNN) -- Police alternately closed and reopened commuter train stations in downtown San Francisco Monday after demonstrators gathered to protest recent shootings by the train system's police officers.
Police in helmets and protective gear shut the Civic Center station about 45 minutes after the demonstration began at 5 p.m., making protesters and media crews head for the exits. Soon after, officials also closed the Powell Street BART station but that station was reopened less than an hour later.
The Bay Area Rapid Transit system reported on its Twitter page that all stations were open less than an hour and a half after the demonstration began at the Civic Center station. Then, the Powell Street station was closed again for a time, only to be reopened with the Civic Center station being closed again.