问题 填空题

科普工作者为了探测海底某处的深度,向海底垂直发射超声波,经过4s收到回波信号,海洋中该处深度为________m。(声音在海水中传播速度是1500m/s)。这种方法     (选填“能”或“不能”)用来测量地球和月球之间的距离,因为                        

答案

3000,不能,真空不能传声

:(1)声音从海面传到海底的时间为t=

那么海水的深度为s=vt=1500m/s×2s=3000m,

(2)由于地球与月球之间是真空,而声音不能在真空中传播,所以不能用这种方法测量地球和月球之间的距离.

故答案为:3000;不能;真空不能传声.

阅读理解

School violence is in the headlines again after recent shootings at schools in Pennsylvania, Wisconsin, and Colorado. After hearing the news, it’s natural for students — no matter how old they are or where they go to school — to worry about whether this type of incident may someday happen to them.

So how safe are schools? It’s actually safer to be in a school than in a car. Twice as many 15-to-19-year-olds die in car accidents than in shootings (and that’s all shootings, not just the ones that happen in schools). According to the Centers for Disease Control and Prevention, less than 1% of all homicides (杀人罪) among school-age children happen on school grounds or on the way to and from school. So the vast majority of students will never experience violence at school.

However, some schools have re-evaluated their safety needs in response to the concerns of families and communities. Some now require that guests check in at the office or have more guards on duty. Some schools have fixed metal detectors. Another thing that helps make schools safer is greater awareness of problems like bullying and discrimination. Many schools have practiced programs to fight these problems and to help teachers and administrators know more about protecting students from this type of violence.

The cause of school violence isn’t easy to understand. There is no single reason why students become violent. Some are just copying behavior they’ve seen at home, in the streets, or in video games, movies, or television. There’s one thing experts do agree on, though: Having access to guns or other weapons makes it easier for some people to lash out against the things or people they don’t like.

小题1:Which of the following statements can prove that schools are safe?

A.About 99% of 15- to-19-year-olds are safe at school.

B.Fewer students have died in car accidents than in shootings.

C.Students shot to death at school are half of all students.

D.Fatal shootings of students are less than 1% of all homicides.小题2: After schools have re-evaluated their safety needs, ________.

A.families will be more concerned about schools

B.communities will be responsible for schools

C.teachers will pay more attention to shootings

D.administrators will arrange to have more guards on duty小题3:From the last paragraph we can conclude that ______.

A.experts have found no reason for school violence

B.students with weapons are easily upset about things

C.school violence could be copied from violence in society

D.no single reason makes students violent小题4:We could probably see this passage in ______.

A.an analysis report

B.a realistic novel

C.a case investigation

D.a news journal

多项选择题