A:what
B:where
C:how
D:why
设集合S={A0,A1,A2,A3},在S上定义运算为:Ai⊕Aj=AK其中k为i+j被4除的余数,i、j=0,1,2,3.满足关系式=x⊕xA2=A0的x(x∈S)的个数为( )
_________ is scientific knowledge used in practical ways in industry, for example, in making new machines.
设集合A=x|x-a<2,B=x|2x-1x+2<1,若A⊆B,则a的取值范围是( )
加热某种固体有气体产生,对于这一变化的分析正确的是( )