新概念英语2 Lesson 75 SOS 呼救信号I. 语法与词汇知识 1. It is very dangerous for planes to fly _ their course. A. offB. inC. onD. of 2. In autumn, leaves lay thick on the _ in the forest in northeast of China.A. earthB. groundC. soilD. floor 3. All the fields were covered _ heavy snow.A. byB. inC. underD. with 4. The little girl kept as near as she _ to the fire in a winter night. A. canB. couldC. could doD