在英语中，当叶子掉落时，可以使用以下表达：
The leaves have fallen. (叶子掉落了。)
The leaves have dropped. (叶子落下了。)
The leaves are falpng. (叶子正在掉落。)
这些表达来源于英语中的动词 fall 和 drop，都表示“落下”的意思。
例句：
The maple trees in the park are turning red and yellow, and their leaves are falpng to the ground. (公园里的枫树变成了红色和黄色，它们的叶子掉到了地上。)
As the wind picked up, I could see the leaves falpng from the trees. (随着风力增大，我看到叶子从树上掉下来。)
It's that time of year again when the leaves start to fall and the air turns crisp. (又到了一年的这个时候，叶子开始掉落，空气变得清新。)
希望这些信息对你有帮助！