A:河流蜿蜒曲折
B:山河相间分布
C:地势西高东低
D:地形复杂多样
已知单位向量a、b,满足a⊥b,则函数fx=xa+b2(x∈R)( )
在下列分类单位中,生物之间性状差异程度最小的是( )
Before I watched ____ 3-D film Life of Pi, I had never seen ______ wonderful film like this.