A:在氮化铝的合成反应中,N2是还原剂,Al2O3氧化剂
B:上述反应中每生成2molAlN,N2得到3mol电子
C:氮化铝中氮元素的化合价为-3
D:C被还原生成CO
已知集合A=1,2,3,4,5,B=x,y|x∈A,y∈A,x-y∈A,则B中所含元素个数为( )
European football is played in about 80 countries, ____ (make) it the most popular sport in the world.