题目内容：
根据下列短文，回答题。Singing Alarms Could Save the BlindIf 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 change all that 51 directional sound alarms capable of guiding you to the exit.
Sound Alert, a company 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. 54 produce a wide range of frequencies that enable the brain to determine where the 55 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 57 people say sounds like static on the radio,” she says.“Its life-saving potential is great. ”She conducted an experiment in which people were filmed by thermal-imaging cameras trying to find their way out of a large 58 room. It 59 them nearly four minutes to find the door 60 a sound alarm, but 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 more easily than the source of a narrow band. Alarms 63 the same concept have already been installed on emergency vehicles.
The alarms will also include rising or falling frequencies to indicate whether people should go up 64 down stairs. They were 65 with the aid of a large grant from British Nuclear Fuels.回答第51空。 A．A without
B．B with
C．C having
D．D selling
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