原因状语从句,在写大作文论证时，经常要说明某事或现象的原因，这时可用原因状语从句。
引导原因状语从句的从属连词有because(因为), as(由于), since(既然),now(that)(既然), when(既然), seeing(that)(由于，鉴于),considering(that)(考虑到), given(that)(考虑到), for(为)等。
1.because引导的原因状语从句一般放于主句的后面，because从句位于句首时要用逗号分开，放在句末时，可不用逗号分开。
《剑桥雅思真题7》Test 1 Passage 2
More than 20% of all freshwater fish species are now threatened or endangered because dams and water withdrawals have destroyed the free-flowing river ecosystems where they thrive.
超过20%的淡水鱼现在受到威胁或濒临灭绝，因为水坝和取水破坏了它们赖以生存的自由流动的河流生态系统。
《剑桥雅思真题8》Test 2 Passage 3
Odours, unlike colours, for instance, cannot be named in many languages because the specific vocabulary simply doesn't exist.
例如，气味不同于颜色，在许多语言中无法命名，因为特定的词汇根本不存在。
2.since引导的原因状语从句。
《剑桥雅思真题7》Test 1 Passage 1
It is technically incorrect to talk about bat ‘radar', since they do not use radio waves.
技术上说蝙蝠“雷达”是不正确的，因为它们不使用无线电波。
《剑桥雅思真题8》Test 3 Passage 1
Safety is a basic requirement since no one wants to put themselves or their expensive equipment at risk.
安全是一项基本要求，因为没有人愿意把自己或昂贵的设备置于危险之中。
3.as引导原因状语从句，位置较为灵活(常放于主句之前)。
《剑桥雅思真题8》Test 4 Passage 1
Pupils mark their own homework: this is an important principle in Japanese schooling as it enables pupils to see where and why they made a mistake, so that these can be avoided in future.
学生们给自己的作业打分：这是日本学校的一个重要原则，因为它能让学生看到他们在哪里犯了错误，为什么犯了错误，以便将来可以避免这些错误。
《剑桥雅思真题10》Test 4 Passage 2
Unfortunately, he was miserable as his research wasn't compatible with his curiosity about healing.
不幸的是，他很痛苦，因为他的研究与他对治疗的好奇心不相符。
4.for引导的并列句只能放于主句之后，并且必须用逗号将其与主句隔开。
《剑桥雅思真题8》Test 3 Passage 2
We may disagree with the ‘general', for we doubt if all musicians of genius could have become scientists of genius or vice versa.
我们可能不同意“通常状况”，因为我们怀疑是否所有天才音乐家都能成为天才科学家，反之亦然。
《剑桥雅思真题9》Test 1 Passage 3
However, they are, in one respect, less fully given back to the water than whales or dugongs, for turtles still lay their eggs on beaches.
然而，在某种程度上，它们比鲸鱼或儒艮更少地回到水中，因为海龟仍然在海滩上产卵。
5.seeing that引导。
Seeing that nobody was very enthusiastic about it, they decided to cancel the trip.
由于没有人有此热情，他们决定取消这次远足。
6.considering that引导。
Google's low product searches are less surprising considering that its product search isn't nearly as expansive as Amazon's.
谷歌的产品搜索量低并不奇怪，因为它的产品搜索并不如亚马逊的范围宽广。
7.now that引导。
《剑桥雅思真题6》Test 4 Section 2
Now that everyone knows what team they're in, we'll get on with the orientation and training programme.
由于每个人都知道他们是哪个队的，我们就继续进行训练。
《剑桥雅思真题8》Test A Writing Sample 1
We just couldn't go on living in the two-bedroom bungalow now thatthe twins are growing up and the new baby has arrived.
我们不能继续住在两居室的平房里，因为双胞胎已经长大了，孩子也出生了。
《剑桥雅思真题11》Test 4 Passage 1
Now that we're actually able to look at the DNA and see where the pencil writings are, it's sort of a whole new world
现在我们可以看到DNA，看到铅笔的笔迹，这是一个全新的世界。
《剑桥雅思真题12》Test 5 Passage 2
They may feel empty, now that the goal that drove them on has gone.
因为驱使他们前进的目标已经没有了，他们可能会感到空虚。
