最近学校里发生了几起奇怪的事件。

There have been several unusual ___occurrences at the school recently.

这个城市交通事故的发生率近年来有所下降。

The ___occurrences of traffic accidents in this city have decreased in recent years.

这种植物在该地区的出现非常罕见。

The ___occurrence of this plant in the area is very rare.