free occurrence

例句：

1. 1. The free occurrence of the disease is a concern for public health officials.
   这种疾病的免费发生是公共卫生官员的关注点。
2. 2.The free occurrence of this phenomenon has led to many debates about its causes.
   这种现象的免费发生引发了许多关于其原因的辩论。
3. 3. The free occurrence of this phenomenon has raised questions about the role of natural disasters in shaping our world.
   这种现象的免费发生引发了对自然灾害在塑造我们世界中所起作用的疑问。