题目内容：
Singing Alarms Could Save the Blind If you cannot see, you may not be able to find your way out of a burning building -and that could be fatal. A company in Leeds could______________(51) all that with directional (定向的) sound alarms capable of guiding you to the exit.Sound Alert, a company run______________(52) the University of Leeds, is installing the alarms in a residential home for______________(53) people in Sommerset and a resource centre for the blind in Cumbria. The alarms produce a ______________ (54) range of frequencies that enable the brain to______________(55) where the sound is coming from.
Deborah Withington of Sound Alert says that the alarms use most of the frequencies that can be______________(56) by humans. "It is a burst of white noise that people say sounds like static (静电噪音) on the radio," she says. "Its life-saving potential is ______________(57)."
She conducted an experiment in which people were filmed by thermal-imaging (热效应成像) cameras trying to find their______________(58) out of a large smoke-filled room. It______________(59) them nearly four minutes to find the door without a sound alarm,______________(60) only 15 seconds with one.
Withington studies how the brain______________(61) sounds at the university. She says that the______________(62) of a wide band of frequencies can be pinpointed (精确地确定) more easily than the source of a narrow band. Alarms______________(63) on the same concept have already been installed on emergency vehicles.
The alarms will also include rising or falling frequencies to ______________(64) whether people should go up or down stairs. They were______________(65) with the aid of a large grant from British Nuclear Fuels. A．change
B．cure
C．demand
D．set
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