阅读短文，回答问题。

Bear Amy,

   I want to be your friend. Let me introduce my family to you. My father is a doctor. He is tall and strong. My mother is a teacher. She is think and kind. My brother Sam is 6 years old. He's short and funny. We live in a big city. However, we usually go hiking on the weekends. I have a small and nice room. There is a bed and a desk in my room. I like reading books. I have many books on my desk. Welcome to my home.

                                                                                                                                                                        Yours,

                                                                                                                                                                          Lucy

有关声的利用可分为两类：____和____。外科医生可以用超声波除去人体内的结石，是利用了声波能传递____。中国传统中医用望、闻、问、切的方法检查病人，其中“闻”就是____的意思，它是利用声波能传递____。

我国草地退化除了气候____，生态环境脆弱；全球变暖；鼠害、虫害严重等自然方面外，还有____，过度开垦，乱采滥挖发菜，人工管理少，____等人为原因。