铁路工人用铁锤敲击铁轨，从异常的声音中发现松动的螺栓，这是利用声音来传递____
题型：填空题
问题：
铁路工人用铁锤敲击铁轨，从异常的声音中发现松动的螺栓，这是利用声音来传递_____________。如果在靠近居民区的工地里进行施工爆破，可观察到附近房屋的玻璃会不停的振动，这说明了声音能传递____。
题型：填空题
阅读理解。
Until the 1980s, the American homeless population comprised (组成) mainly older males. Today,
homelessness strikes much younger part of society. In fact, a 25-city survey by the U. S. Conference of
Mayors in 1987 found that families with children make up the fastest growing part of the homeless
population. Many homeless children gather in inner cities; this transient(变化无常的) and frequently
frightened student population creates additional problems - both legal and educational - for already
overburdened(负担过重的)urban school administrators and teachers.
Estimates of the number of homeless Americans range from 350,000 to three million. Likewise,
estimates of the number of homeless school children vary radically. A U.S. Department of Education
report, based on state estimates, states that there are 220,000 homeless school-age children, about a
third of whom do not attend school on a regular basis, But the National Coalition for the Homeless
estimates that there are at least two times as many homeless children, and that less than half of them
attend school regularly.
One part of the homeless population that is particularly difficult to count consists of th
e "throwaway"
youths who have been cast of their homes. The Elementary School Center in New York City estimates
that there are 1.5 million of them, many of whom are not counted as children because they do not stay in
family shelters and tend to live by themselves on 
the stre
ets.
Federal law, the Stewart B. McKinney Homeless Assistance Act of 1987, includes a section that
addresses the educational needs of homeless children. The educational p
rovisions of the McKinney Act
are based on the belief that all homeless children have the right to a free, appropriate education.
1. It is implied in the first paragraph that ____.
A. the writer himself is homeless, even in his eighties
B. many older homeless residents are going on strike in 25 cities
C. there is a serious shortage of academic facilities (设施).
D. homeless children are denied the opportunity of receiving free education
2. The National Coalition for the homeless believes that the number of homeless children is _____.
A. 350,000
B. 1,500,000
C. 440,000
D. 110
,000
3. One part of the homeless population is difficult to estimate. The reason might well be ____.
A. the homeless children are too young to be counted as children
B. the homeless population is growing rapidly
C. the homeless children usually stay outside school
D. some homeless children are deserted by their families
4. The McKinney Act is mentioned in this passage in order to show that ___.
A. the educational problems of homeless children are being recognized
B. the estimates on homeless children are hard to determine
C. the address of grade-school children should be located
D. all homeless people are entitled(有权利的) to free education
5. The passage mainly deals with ____.
A. the legal problems of the homeless children
B. the educational problems of homeles
s children
C. the social status of older males
D. estimates on 
the homeless population