A:16
B:16π
C:4
D:4π
已知a,b,c∈R,则2a2+3b2+6c2=1是a+b+c∈﹣1,1的( )
It's very convenient ______ us to buy train tickets now because we can buy them either from the station or on the Internet.
关于食物消化的叙述,错误的是( )
已知某粗盐样品中含有泥沙和Na2SO4、MgCl2、CaCl2等杂质.实验室提纯氯化钠的流程如下: