— were you yesterday?
— I was at school.
A:What
B:Where
如图所示,一束光线从空气斜射到水面时发生反射和折射,OB为反射光线,请作出入射光线和大致的折射光线方向.
研究表明,世界文化潮流有一个规律,那就是世界各国跟着世界经济前三名走。这一研究成果显示( )