occur
单词辨析：
普通用词，多用于偶然事件。
The accident happened at 5 o'clock.
事故发生在5点钟。
What happened then?
后来又发生了什么事？
可用于偶然事件或计划之事，可与 happen 换用。
The earthquake occurred/happened at dawn.
地震发生在黎明时分。
A serious traffic accident occurred/happened yesterday.
昨天发生了一起严重的交通事故。
主要用于事先计划好的事情。
Great changes have taken place in China.
中国发生了翻天覆地的变化。
The parade will take place on Sunday, rain or shine.
庆祝游行定于星期日举行，风雨无阻。
相关例句：
No one has suggested how this might occur
没人说得清这事是怎么发生的。
High levels of nitrate occur in eastern England because of the heavy use of fertilizers.
英格兰东部因大量使用化肥导致土壤硝酸盐浓度过高。
The time when a solar eclipse will occur can be calculated.
日食发生的时间可以推算出来。
It did not occur to me to check my insurance policy
我没有想到要核实我的保险单条款。
The cattle disease occurs more or less anywhere in Africa where the fly occurs
在非洲凡是有这种蝇虫的地方，几乎都会出现这一牛病。
Dryness at the roots can occur very easily specially when plants are grown in containers.
根部很容易干枯，特别是当植株被种养在盆中时。