A:①③④
B:②③④
C:①②④
D:①②③
钾长石是常见的含铝矿物,其主要成分是KAlSi3O8,KAlSi3O8中硅元素的化合价为( )
给出一列数11,12,21,13,22,31,⋯,1k,2k-13k-2,⋯,k1,⋯,在这列数中,第50个值等于1的项的序号是( )
Another new year is coming. It's up to all of us to fill it with things____ promise progress and happiness.