对于n个元素的关键字序列{ki,k2,…，kn},当且仅当满足关系ki≤k2i且ki≤k2i+i(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
正确答案是D