线从空气进入玻璃时会发生的现象是（）。

GPS全球定位系统是（）由美国提出的。A.1970年B.1973年C.1995年D.1996年

单项选择题GPS全球定位系统是（）由美国提出的。

Every day some people are killed while they are crossin...

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．

子午仪卫星导航采用（）这种方法定位。A.融合导航定位B.多普勒测速定位C.测距导航定位D.组合法定位

单项选择题子午仪卫星导航采用（）这种方法定位。