He made up his mind to devote his life________ pollution ________happily.
已知A-1,0,B1,0两点,过动点M作x轴的垂线,垂足为N,若MN→2=λAN→·NB→,当λ<0时,动点M的轨迹为( )
喜马拉雅山脉主要是由____板块和____板块相互碰撞挤压形成的.