单项选择题 GPS全球定位系统是（）由美国提出的。

填空题 Every day some people are killed while they are crossing the roads．Most of these people are old people and children．Old people are often killed because they can’t see or（）very well．Children are killed because they are not（）．They forget to look and listen before they（）the roads．A car or a bus can’t stop（）．If a car is going very fast，it will travel many metres（）it stops．Some people don’t always understand this．

单项选择题 子午仪卫星导航采用（）这种方法定位。