题目

There was once a farmer. He lived near a road. It was not a busy road, but from time to time cars passed the farm. Near the farm gate, there was a large hole in the road. The hole was always full of water, and the drivers of the cars could not see how deep the hole was. They thought that it was not deep.Then when they drove their cars into the hole, they could not drive out of it because it was so deep. The farmer didn’t spend much time working on his farm. He spent most of it watching the hole. When a car drove into it, he pulled the car out with his tractor and asked the driver a lot of mo宋代史书记载：“舟师识地理，夜则观星，昼则观日，阴晦则观指南针。”对此材料的理解最准确的是( )A. 宋代的航海完全依靠指南针来辨别方向B. 我国劳动人民最早知道了磁针指南的作用C. 指南针在北宋时用于航海事业，但只是辅助作用D. 指南针是我国古代水手最早发明的