题目

设数列满足,且对任意的,点都有,则的前项和为(    )  A.            B.           C.          D. 答案：AGetting lost while camping and hiking is probably the biggest problem most campers face. It’s a good idea to learn how to use a compass and map to get from place to place.   60  . To avoid getting lost, stay on well-marked paths and never camp without a friend or family member along for the ride. Before you start on your adventure, get maps from the park or forest ranger (护林员).   61  , follow path markers to the nearest ranger station and wait for help to arrive. If you can't find a ranger station, look for a safe place and wait for help to come looking for you. People will find you if you've followed procedures such as signing in on paths and leaving information at home on where you'll be. An ordinary sports whistle (口哨) is a camper's best friend when it comes to calling for help.   62  . If you have a cell phone and can get a signal (信号), try reaching park rangers by phone. Once you have an unexpected problem, no matter how small it seems to you, ask park rangers for help.   63  , take along a parent or other relative. Sharing the beauty of the great outdoors can actually help you get to know the adults in your life better, without all the usual distractions (分心) of life. A great camping trip not only leaves you with memories to treasure, it may start you on a lifelong hobby. A. If you really want to head for the hills and none of your friends are into it B. However, most campers have no idea how to use a compass C. Unluckily, most campers don’t follow these steps D. The whistle will be heard at distances the human voice can't travel E. If you and your friend do get lost