题目

中国“蛟龙”号深潜器目前最大深潜极限为7062.68米．如图，某天该深潜器在海面下2000米的A点处作业，测得俯角为30°正前方的海底C点处有黑匣子信号发出．该深潜器受外力作用可继续在同一深度直线航行3000米后，再次在B点处测得俯角为45°正前方的海底C点处有黑匣子信号发出，请通过计算判断“蛟龙”号能否在保证安全的情况下打捞海底黑匣子．（参考数据≈1.732） The students in America usually begin high school at the age of 13 or 14. Some leave at the age of 16. But most finish the 4-year high school study. They do not get their first full-time work or begin college studies until they are 17 or 18 years old. The high school day is about 7 hours long. Part of the day is made into classes of about 50 minutes long. The students have lunch in the middle of the day. American students study English, history, math, science, art and languages. Some also learn job skills. They can learn how to use a computer or how to mend a car. Other students may learn by working in an office, a hospital or other places one day a week. Jean Wilton Anderson is 16 years old. She lives with her parents and 2 younger brothers in Bethesda, Maryland, near Washington D.C. Jean studies at Whitman High School. There are about 1500 students at the school. Most of them will go up to colleges. Jean wakes up early every morning. She begins school at about 7:30. This is her third year of high school. Every day she takes classes to learn English, world history, physics and trigonometry. （三角）She also has a class about different religions（宗教）. And she plays the violin in music classes. School ends at about 2 o’clock in the afternoon. Yet, Jean stays 2 or more hours longer every day for sports. Jean arrives home at about 5 o’clock in the afternoon. She eats dinner. Then she starts her homework. She also spends a lot of time talking on the telephone with her friends. Students in America have their way of talking. They use the word “like” all the time. Jean and her girlfriends wear blue jeans and shirts or sweaters every day. The boys at her school also wear blue jeans. But they like to wear blue jeans that are several sizes too large for them. Like students of her age in most part of the country, Jean began driving a car when she was 16 years old. She does not have her car. Most of the students in high school have their own car. Many of them drive their cars to school every day. 1. When the students in America finish their high school, they ________. A. are usually 17 or 18 years old          B. try to find the full-time work C. all begin their college studies            D. are ready to leave the country 2. Jean Wilton Anderson _________. A. has a four-people family                         B. lives in the city of Washington C. has studied in her school for 3 years              D. will go up to a college 3. On a school day Jean Wilton Anderson ___________. A. has to get to school before 7:30 in the morning B. takes classes for 10 subjects in the school C. does some sports and homework after class D. Spends hours on the phone with her classmates 4. Which of the following is NOT true? A. Students in high schools use the word “like” very often. B. The boy students wear blue jeans as the girls. C. Many high school students go to school in their own car. D. Boy students wear jeans of larger size because they grow fast.