三、重点句型
1. We human beings could not survive without all the plants and animals around us.
没有周围的动物和植物，我们人类就无法生存。
介词短语without在这里表示假设条件，相当于if there were no plants or animals around us.有时虚拟条件不用从句而用介词短语来表示。例如：
Without her help, the police couldn’t have succeeded in solving the mystery in such
a short time.如果没有她的帮助，警察不可能在这么短的时间内破了这个疑案。
But for the storm, we could have arrived here earlier.
要不是那场暴风雨，我们早就到这里了。
We could have done better under more favorable conditions.
在更有利的条件下我们还可以做得更好。
2. If we know more about what causes endangerment, we may be able to take measures
before it is too late.如果我们能更多地了解致使生物濒危的原因，就能及时采取补救措施。
before 趁…..（还没有）。例如：
They are thinking of buying the house before the prices go up.
他们正在考虑趁房价未涨时把房子买下来。
If you don’t like the present job, I suggest you look for another one before it is
too late.
如果你不喜欢目前的工作，我建议你趁早另谋出路。
3. A species can become endangered for different reasons.物种濒临危险有各种原因。
endanger危害、危及（某人/某事物）；使遭到危险 (cause danger to sb / sth; put sb /sth in danger)。例如：
The polluted air in the city is badly endangering the health of the people.
城市中被污染的空气严重地危及人民的健康。
Drunk-driving can not only cause traffic accidents, but also endanger the lives of
pedestrians. 酒后驾车不仅会造成交通事故，而且会危害到行人的生命。