题目

如图，篮球架下的运动员原地垂直起跳扣篮，离地后重心上升的最大高度为H，上升第一个所用的时间为t1，第五个所用的时间为t2，不计空气阻力，则满足： A. B. C. D.4 << 5 答案：【答案】D【解析】逆向分析可以看作是自由落体运动，根据初速度为零的匀加速直线运动中，连续相等的位移内时间之比等于1：(−1)：(−)：(2−)：(−2)……可得：，故4 << 5A．，与结论不相符，选项A错误； B． ，与结论不相符，选项B错误； C． ，与结论不相符，选项C错误； D．4 << 5，与结论 阅读下面短文并回答问题，然后将答案写到相应的位置上(请注意问题后的词数要求)。 　　(1)The British summer is extremely beautiful．Trees, flowers, birds and butterflies make the whole country like a big garden．However, many British people have noticed that butterflies have been gradually disappearing from this picturesque scenery during the past several years．What has happened to them? 　　(2)Butterfly Conservation, a charity in the UK, is running a survey to help answer this question．The result is more serious than people expected．According to the survey, among 59 butterfly species found in Britain, more than three quarters of them are suffering a declining population, including the most popular ones．What's more, half of all butterfly species are in the danger of dying out．Some common species such as the small Tortoiseshell butterfly and the Wall butterfly are dropping dramatically．The latter cannot even be seen in many parts of central and southern England．The Blue butterfly was commonly seen in the south．However, it has started colonizing(迁徙至)Edinburgh in the past few years． 　　(3)The numbers of butterflies have dropped to a record low in the past three years largely because the summer in the UK is getting cooler and their habitat is also worsening．Fortunately Britain is experiencing a long hot summer this year compared to the last few summers．Conservationists believe the warm weather will bring some benefit to the butterflies． 　　(4)Sir David Attenborough, president of Butterfly Conservation, said：“Large quantities of butterflies tell us that all is well with nature．When they decline it's a warning that other wildlife will be soon ________．” 　　(5)The survey is still going on．The public are also encouraged to keep track of the UK's butterfly population．The organizers hope the survey will help raise public awareness of the value of butterflies in the UK．Butterflies give an indication of the well-being of nature and the environment． 1．What is the best title of the passage?(no more than 10 words) ________________ 2．List two reasons for butterflies’ reduction in number．(no more than 10 words) ①________ ②________ 3．Complete the following statement with proper words．(no more than 4 words) But a large number of British people have realized that butterflies ________ from the beautiful scenery since a few years ago． 4．Fill in the blank in Paragraph 4 with proper words．(no more than 5 words) 5．What does the underlined word “them”(paragraph 2)probably refer to?(no more than 4 words)