Pollution has done great harm to ____(live) things on the earth.
下列粒子由一个原子获得两个电子而形成的是( )
我国人口分布不均,其特点是( )
一 Nowadays most young people _____ sending short messages ____ notes.
一 After all, science is developing faster and faster.
(Ⅰ)求证:FG∥面ADD1A1;
(Ⅱ)求二面角B﹣EF﹣C的余弦值.