occur

1. V-I When something occurs, it happens. 发生

If headaches only occur at night, lack of fresh air and oxygen is often the cause. 如果头痛只发生在晚上，缺少新鲜空气和氧气常常是其原因。

The crash occurred when the crew shut down the wrong engine. 机组人员关错发动机后就坠毁了。

2. V-I When something occurs in a particular place, it exists or is present there. (某事物在某地) 出现

These snails do not occur on low-lying coral islands. 这些蜗牛不会出现在低洼的珊瑚岛上。

3. V-I If a thought or idea occurs to you, you suddenly think of it or realize it. (想法、主意在某人脑海中) 突然出现[no passive, no cont]

It did not occur to me to check my insurance policy. 我没想到要核对我的保险单。