平面上4条直线相交,交点的个数是( )
A:1个或4个
B:3个或4个
C:1个、4个或6个
D:1个、3个、4个、5个或6个
Edison is a famous ____(发明家) all over the world.
Tom was so careless that he his right arm when he was riding to school
yesterday.
2011年3月,日本近海强震引发的海啸,造成福岛核电站发生核泄漏事件,导致环境出现碘131超标,碘131原子的核电荷数为53,相对原子质量为131,碘原子的核外电子数为