题目

One night, while surfing the Internet, I happen to find a                           1．            chatting room, there people were talking to each other happily                         2．            in English．I couldn't help chat with some of them．Much to                        3．            my surprised, I found the oral English of some teenagers was                         4．            much better than me．I realized my oral English n已知船在灯塔北偏东处，且船到灯塔的距离为2，船在灯塔北偏西处，两船间的距离为，则船到灯塔的距离为       ；