defining occurrence

例句：

1. 1. The occurrence of a storm can cause traffic congestion.
   暴风雨的发生会导致交通拥堵。
2. 2. The occurrence of this phenomenon has never been observed before.
   这种现象的出现前所未见。
3. 3.The occurrence of the disease is closely related to environmental factors.
   这种疾病的出现与环境因素密切相关。