occur 
英 [əˈkɜː]  美 [əˈkɜr] 
v. 发生；出现；存在

例句：
If headaches only occur at night, lack of fresh air and oxygen is often the cause. 

如果只是晚上头疼，那常常是因为缺乏新鲜空气和氧气。

Most scientists agree that climate change is occurring. 

大多数科学家都同意气候变化正在发生。

The explosion occurred yesterday. 

爆炸发生在昨天。

the chances of an accident occurring 

事故发生的可能性

Racism and sexism occur in all institutions. 

种族歧视和性别歧视在所有制度中都存在。

The phrase occurs often in the Koran. 

这句话经常出现在《古兰经》里。