{{B}}Singing Alarms Could Save the
Blind{{/B}} 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 change all that{{U}} (51) {{/U}}directional sound alarms capable
of guiding you to the exit. Sound Alert, a company{{U}} (52)
{{/U}}the University of Leeds, is installing the alarms in a residential
home for{{U}} (53) {{/U}}people in Sommerset and a resource centre for
the blind in Cumbria. {{U}}(54) {{/U}} produce a wide range of
frequencies that enable the brain to determine where the{{U}} (55)
{{/U}}is coming from. Deborah Withington of Sound Alert says
that the alarms use most of the frequencies that can be{{U}} (56) {{/U}}
by humans. "It is a burst of white noise {{U}}(57) {{/U}}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{{U}} (58)
{{/U}}room. It{{U}} (59) {{/U}}them nearly four minutes to find the
door {{U}}(60) {{/U}}a sound alarm, but only 15 seconds with
one. Withington studies how the brain {{U}}(61)
{{/U}}sounds at the university. She says that the {{U}}(62) {{/U}}
of a wide band of frequencies can be pinpointed more easily than the source of a
narrow band. Alarms{{U}} (63) {{/U}}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{{U}}
(64) {{/U}}down stairs. They were{{U}} (65) {{/U}}with the aid
of a large grant from British Nuclear Fuels.
【答案解析】句子中的more... than表示该句是对两样事物的对比。than后面是the source of a narrow band，这里的narrow和前半句的wide形成反比，从上下文中可以看出，the source of a narrow band of(frequencies)是和the source of a wide band of frequencies形成对比。
【正确答案】
D
【答案解析】这个句子有主语alarms，有谓语have been installed，这里应填入动词的分词形式。be based on是常用的搭配，所以，应选择动词的过去分词形式。选项A的basis是名词，明显是错的。
【正确答案】
A
【答案解析】根据上半句中的rising or falling frequencies，这里应填入or，与上半句表达的意思相一致。音频升高表示上楼，音频降低表示下楼。