一个有 n 个结点的连通图的生成树是原图的极小连通子图，且包含原图中的所有 n 个结点，并且有保持图联通的最少的边。-An n-node connected graph of the minimal spanning tree is the original connected subgraph, and contains all the n original nodes, and there are plans to maintain at least the edge of Unicom.