diameter of a connected graph

例句：

1. 1.The diameter of the tree is about5 meters.
   这棵树的直径大约是5米。
2. 2. The circumferenceof the circle is twice its diameter.
   圆的周长是直径的两倍。
3. 3.The radius of the circle is half thediameter.
   圆的半径是直径的一半。