If you look here at the dots, compare node B in the upper left to node D in the far right; B has four friends coming out from him and D has six friends coming out from him.
如果你仔细看看这些圆点， 把左上角的点B 和最右边的点D做比较。 B有四个朋友从他那里延伸出来， D则是有六个朋友。