happen / take place / occur / come about / break out 意为“发生”

1. happen 表示“发生，碰巧”，一般用于偶然或突发性事件。常用的结构是：It happens that...和happen to do sth，分别意为“碰巧...”“碰巧做某事”。

2. take place 表示“发生，举行，举办”，一般指非偶然性事件，即这种事件的发生一定有某种原因或事先的安排。

3. occur 作“发生，想到，突然想起”解，其意义相当于happen。常用结构有sth occurs to sb/it occurs to sb that...“某人突然想起...”。

4. come about 表示“发生，产生”，多指事情已经发生了，但还不知道为什么，常用于疑问句和否定句。

5. break out 意为“发生，爆发”，常指战争、灾难、疾病或者争吵等事件的发生，也可以表示突然大声喊叫等。

全部

1·When exactly did the incident occur?

这一事件究竟是什么时候发生的？《牛津词典》

2·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。《柯林斯英汉双解大词典》

3·Rattlesnakes occur in the warmer, drier parts of North America.

响尾蛇出现在北美温暖干燥的地区。《牛津词典》

4·Nitrates are chemicals that occur naturally in water and the soil.

硝酸盐是水和土壤里天然存在的化学物质。《柯林斯英汉双解大词典》

5·Such events occur only when the external conditions are favourable.

此类事件只有当外界条件有利时才会发生。《柯林斯英汉双解大词典》

6·Ulcers occur when the stomach's natural acids eat into the lining of the stomach.

胃酸腐蚀胃壁时，就出现了溃疡。《柯林斯英汉双解大词典》

7·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。《柯林斯英汉双解大词典》

8·If the climate gets drier, then the logical conclusion is that even more drought will occur.

如果气候变得更干燥，那么符合逻辑的结论就是甚至更多的旱灾将会发生。《柯林斯英汉双解大词典》

9·Scientists warned that emergency cooling systems could fail and a reactor meltdown could occur.

科学家们警告说紧急冷却系统可能失灵，核反应堆的堆芯熔毁可能会发生。《柯林斯英汉双解大词典》

10·Within a half-mile from ground zero, death from radiation poisoning will occur within twelve hours.

在核爆点半英里内，辐射中毒引起的死亡会在十二小时内发生。《柯林斯英汉双解大词典》

发生

1·When exactly did the incident occur?

这一事件究竟是什么时候发生的？《牛津词典》

2·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。《柯林斯英汉双解大词典》

3·If the climate gets drier, then the logical conclusion is that even more drought will occur.

如果气候变得更干燥，那么符合逻辑的结论就是甚至更多的旱灾将会发生。《柯林斯英汉双解大词典》

4·Within a half-mile from ground zero, death from radiation poisoning will occur within twelve hours.

在核爆点半英里内，辐射中毒引起的死亡会在十二小时内发生。《柯林斯英汉双解大词典》

5·Most volcanoes occur at plate boundaries.

大多数火山的爆发发生在板块边界。

出现

1·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。《柯林斯英汉双解大词典》

2·Rattlesnakes occur in the warmer, drier parts of North America.

响尾蛇出现在北美温暖干燥的地区。《牛津词典》

3·Ulcers occur when the stomach's natural acids eat into the lining of the stomach.

胃酸腐蚀胃壁时，就出现了溃疡。《柯林斯英汉双解大词典》

4·Where does extreme poverty occur?

极端贫困出现在哪里？

5·Frosts often occur in November.

11月份经常出现霜冻。《新英汉大辞典》

存在

1·Nitrates are chemicals that occur naturally in water and the soil.

硝酸盐是水和土壤里天然存在的化学物质。《柯林斯英汉双解大词典》

2·Does it look like something that might occur in nature?

这看起来像自然界中可能存在的事物吗？

3·They're more likely to occur in societies that frown on divorce.

这种关系更可能存在于反对离婚的社会中。

4·They occur on a wide range of soil types and in extremes of climate.

它们广泛存在于各种土壤类型和极端气候中。

5·Exclusive care by the male parent is much less common, but it does occur.

由男性家长单独照顾的情况要少得多，但这种情况确实存在。

(1)occur as以...的形式出现

(1)occur for发生在…时候