A:培育良种牛,并加强对牛群病害的研究
B:天然草场和人工草场相结合,实行轮荒制度
C:大力开垦草原,种植饲料作物
D:往牧区外迁移人口,使牧区更有利于大规模生产
Cathy was born blind(天生是盲的), so she has __________ seen our beautiful world.
与向量a→=(12,5)平行的单位向量为( )