grey hole

例句：

1. 1. The old tree has a grey hole in its trunk.
   那棵老树树干里有一道灰色的洞。
2. 2.The cave was filled with grey holes that led to nowhere.
   这个洞穴里满是灰色的洞，没有出路。
3. 3. The grey hole in the wall is where the rats come out at night.
   墙上的那个灰色洞是老鼠晚上出来的地方。