问题：
[单选题]
G is a simple undigraph, A is an adjacency matrix of G, M is an associative matrix of G, and D is a diagonal matrix of the degree of the i-th element of the vertex on the diagonal. Their relationship is: G是简单无向图，A为G的邻接矩阵，M为G的关联矩阵，D是对角线上第i个元素为顶点i的度的对角矩阵,它们的关系是：
AA=M
BA+D=MMT
CA+D=MTM
DNot direct relationship 没有直接关系
