A. For extremely high altitude flights. B. For urgent mission to places inaccessible to other kinds of craft. C. For rescue work. D. For high-speed transportation. 参考答案:B 答案解析:关键要注意题目中的“absolutely essential”,文章中第四段提到直升飞机的许多用途,比如可以当作空中办公室(airborne offices),都市里警方用来执行各种任务,直升飞机也可