单项选择题
A．the Public Transit system’s efficiency B．the success of Transit Police program C．the police’s emphasis on security of downtown areas D．the worsening security condition of the area
A．teenagers under 14 are not allowed to visit the White House B．foreigners are less likely to be permitted to tour the White House C．separate tours can also be scheduld for individual visitors D．security is the chief concern in scheduling White House tours
A．keep a close watch over the road ahead B．take pictures of the passengers on board C．increase the efficiency of the transit system D．help the transit police detect criminals