对下列所描述的物理现象解释正确的是（　　）

由于南海岛礁散布，被航海者视为险途，向有“危险地带”之称，有谚云：“走水行船三分命”。于是，一代代船长口口相传，笔笔记录，将航海技术、路线水流、岛屿暗礁分类整理，谱就渔民智慧的结晶——南海航道更路经。据专家考证，南海航道更路经形成于明代，如今，海南的渔民们仍然在实践中补充丰富着南海航道更路经。

阅读短文, 选择正确答案。

     I am an English girl. My name is Kate Green. I am thirteen. I am at school now. Look! This is my school. It is Hongda School. I am in Class Eight. I am in Row Four. I am in Team Six. I am Number Five. At school I have a good friend. She is a girl, too. Her name is Ann. She isn’t at school today. I think she is at home. My teacher's name is Mr. Smith. He is a very good teacher. Today he wears (穿) a new T-shirt. He looks very young. I don't know his age. But I think he is old, because （因为）he has a son and a daughter. His son is a doctor and his daughter is a policewoman.