对于n个元素的关键字序列{k1,k2,..., kn} ,当且仅当满足关系ki≤k2i且ki≤k2i+1(i=1,2, …[n/2] )时称为小根堆(小顶堆)。以下序列中,( )不是小根堆。A.12,20,36,48,25,50,40 B.12,36,20,48,40,25,50 C.12,20,25,36,40,48,50 D.12,36,20,48,25,50,40