变黑

例句：

1. 1. The paint on the wall has blackened over time.
   墙上的油漆随着时间变黑了。
2. 2. The sun had blackened his skin in the desert.
   在沙漠中，太阳使他的皮肤变黑了。
3. 3.The old tree was so old that its bark had blackened and cracked.
   那棵老树太老了，它的树皮都变黑并且开裂了。