1、When these side effectsoccur, they are called adverse reactions.(当这些副作用发生时，它们被称为不良反应。)
2、Rattlesnakesoccur in the warmer, drier parts of North America.(响尾蛇出现在北美温暖干燥的地区。)
3、When exactly did the incidentoccur?(这一事件究竟是什么时候发生的？)
4、Does it look like something that mightoccur in nature?(它看起来像自然界中可能发生的事情吗？)
5、Most volcanoesoccur at plate boundaries.(大多数火山的爆发发生在板块边界。)
6、If Dollo's law is right, atavisms shouldoccur only very rarely.(如果多洛定律是正确的，返祖现象应该很少发生。)
7、These snails do notoccur on low-lying coral islands.(这些蜗牛不会出现在低洼的珊瑚岛上。)
8、They're more likely tooccur in societies that frown on divorce.(这种关系更可能存在于反对离婚的社会中。)
9、Additional breathing changesoccur during REM sleep that are even more dramatic than the changes thatoccur during NREM.(在快速眼动睡眠期发生的额外的呼吸变化，甚至比那些在非快速眼动期发生的变化还要显著。)
10、Such eventsoccur 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。)
11、Within a half-mile from ground zero, death from radiation poisoning willoccur 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。)
12、Very rarely did any violent crimes actuallyoccur.(暴力犯罪实际上很少发生。)
13、Where did the shark attacksoccur recently?(最近的鲨鱼袭击发生在哪里？)
14、Earthquakes can and dooccur at all depths to about 460 miles.(地震在460英里深度的地方都有可能发生，也确实会发生。)
15、Frosts oftenoccur in November.(11月份经常出现霜冻。)
16、It didn'toccur to her to ask for help.(她没想到请别人帮忙。)
17、Ulcersoccur 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。)
18、How can volcanic activityoccur so far from a plate boundary?(火山活动是如何在离板块边界那么远的地方发生的呢？)
19、Bombings and shootingsoccur almost daily in Thailand's three southernmost provinces.(在泰国最南部的三个省份，爆炸和枪击事件几乎每天都在发生。)
20、Where does extreme povertyoccur?(极端贫困出现在哪里？)
21、Nitrates are chemicals thatoccur naturally in water and the soil.(硝酸盐是水和土壤里天然存在的化学物质。)
22、Scientists warned that emergency cooling systems could fail and a reactor meltdown couldoccur.(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。)
23、Mind it doesn'toccur again!(小心别再发生这种事了！)
24、The time when a solar eclipse willoccur can be calculated.(日食发生的时间可以推算出来。)
25、Why did the near extinction and migrations of wild animalsoccur?(为什么会发生野生动物濒临灭绝和迁徙的现象？)
26、If the climate gets drier, then the logical conclusion is that even more drought willoccur.(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。)
27、The coughing with asthma canoccur during the day or at night.(哮喘咳嗽可发生在白天或晚上。)
28、No one has suggested how this mightoccur.(没有人提议过这事如何开始。)
29、If headaches onlyoccur 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。)
30、Extreme events, however, will continue tooccur.(然而，极端事件将继续发生。)
