如图,在正方体ABCD﹣A1B1C1D1中,P为对角线BD1的三等分点,P到各顶点的距离的不同取值有( )
A:3个
B:4个
C:5个
D:6个
设函数y=f(x)在(-∞,+∞)内有定义,对于给定的正数k,定义函数:fkx=f(x),(f(x)≤k)k,(f(x)>k),取函数f(x)=2-x-e-x,若对任意的x∈(-∞,+ ∞),恒有fk(x)=f(x),则( )
将撒哈拉以南非洲相关知识填写到下面框图中.
A.人口增长过快,粮食生产落后
B.生态环境恶化
C.开垦草原
D.粮食不足.
某同学在制作洋葱表皮细胞临时装片时进行了如图所示的操作,图中操作不正确的是( )
— How nice the fish tastes! Could you tell me who taught you to cook it?
— I learnt it _______watching TV. I learn to cook many dishes_______ TV.