题目

This is Hong Kong Middle School. It is very big and beautiful. There are 34 classes, 300 teachers and 3, 500 students in the school. In the middle of the school there is a tall building. It’s for us to have classes. All the classrooms are there. There are some small rooms, too. They are offices for the teachers to work. All the teachers get ready for their lessons there. In front of the tall building, there is a small one. It is the library. There are many books there. The teachers and the students like to read books in it. Sometimes they borrow(借)books from it. There is a dining hall behi两人相距较远说话时，听不到对方的声音，但同样情况下，用自制的土电话就可以听到相互的说话声；耳朵贴在铁轨上能听到远处火车开来的声音而站起来就听不到了．对此，请你提出一个要研究的问题：    ．