sour bark

例句：

1. 1. The old tree had a lot of rotten and sour bark.
   这棵老树有许多腐烂和酸的树皮。
2. 2. The scientist found that the sour bark was a good indicator of the tree's health.
   科学家发现酸的树皮是一个很好的树木健康的指示器。
3. 3. The old house needed some repairs to remove the sour bark.
   这所旧房子需要一些修理来去除酸的树皮。