高中英语必修三第四单元重点、难点Unit Four Astronomy: the science of the stars1、They were followed in time by land animals. 陆地动物及时出现。
in time及时；终于A stitch in time saves nine. 小洞不补，大洞尺五。
You will get used to it in time. 最终你会习惯的。
易混辨析：in time和on time in time表示“及时；终于”；而on time表示“按时”。
联想扩展：in no time 立即；马上at one time 曾经；一度at a time 一次at any time 在任何时候at times有时；偶尔from time to time 有时即时活用：– How often do you go to see your parents? --- __________.A. In no timeB. After a whileC. In a short timeD. From time to time 答案：D2、They produced young generally by laying eggs. 它们以产蛋的方式生产后代。
lay eggs 下蛋How many eggs does you hen lay every week? 你的母鸡每周下多少蛋？联想扩展：lay the table 摆桌子lay up 储存；搁置lay over 推迟lay the blame on 责怪lay the foundation 奠定基础lay to 归咎于lay open 摊开；揭露lay out 摆开；展示lay aside 放在一边；积蓄lay down 放下；放弃lay for 等候3、These animals were different from all life forms in the past, because they gave birth to young baby animals and produced milk to feed them.这些动物和以前的任何生物形式都不同，因为它们产仔并用奶水喂养它们。
give birth to…生产；产生She gave birth to a healthy baby last night. 昨晚她生了一个健康的婴儿。
That century gave birth to many great men. 那个世纪产生了许多伟人。
4、These animals were different from all life forms in the past, because they gave birth to young baby animals and produced milk to feed them.这些动物和以前的任何生物形式都不同，因为它们产仔并用奶水喂养它们。
feed vt. 用法归纳：（1）饲养If I am laid-off, I will feed some pigs. 如果下岗，我就养猪。
Do you feed any pets at home? 你在家养宠物吗？特别提示：feed作“饲养”讲时，等于raise 和keep。
（2）喂养We feed grass to sheep. 我们给羊喂草。
We feed sheep with grass. 我们用草喂羊。
特别提示：注意feed当“喂养”讲时动物和饲料的前后顺序关系以及不同介词的用法。
即时活用：1、He______ a lot of chicken______ his farm.A. rises; in B. keeps; on C. raises; in D. supports; on2、– I have a very bad cold.--- Well, have you ever heard of a saying which goes “_______ a cold and starve a fever?”A. feedingB. to feedC. fedD. feed 答案：BD5、Finally about 2.6 million years ago some small clever animals, now with hands and feet, appeared and spread all over the world.最后大约在两百六十万年前，一些有手有脚的小型聪明动物出现了，并且扩散到世界各地。
spread v.用法归纳：（1）传播；传开（vi.）Bad news spreads quickly. 坏消息传的很快。
Word spread that there was a variant virus of H1N1. 消息称H1N1病毒已经产生变异。
（2）铺开；展开(vt.) The bird spread its wings and was about to fly. 鸟伸开翅膀准备要飞。
She spread a new sheet over the bed. 她给床上铺了一个新床单。
（3）涂；抹(vt.) Please spread the paint evenly. 把油漆抹均匀。
It’s better for you to spread the honey on the bread. 你最好把蜂蜜抹在面包上。
（4）伸展；延伸（vi.）Xi’an is spreading to the north and the west. 西安正在向北向西延伸。
The forest spreads from here to the foot of Qinling mountains. 森林从这儿延伸到秦岭山脚下。
联想扩展：spread out 伸开；散开；铺开spread over 覆盖一片；持续spread with 在…上涂抹即时活用：Soon the news ________ across the whole country, ______the people.A. spread; excitingB. spread; excitedC. was spread; excitedD. was spread; exciting 答案：A6、Thus, in their turn, become the most important animals on the planet. 这样，轮到它们成为这个星球最重要的动物。
in one’s tur n轮到某人；接着Please get on the bus in your turn. 该你上车了。
联想扩展：at every turn 事事；经常by turns 轮流go for a turn 散步；除去兜风on the turn 在变质out of turn 不合时宜的take a turn 转弯take turns 轮流to a turn 恰好7、They are putting too much carbon dioxide into the atmosphere, which prevents heat from escaping from the earth into space. 它们向大气层排放大量的二氧化碳，这阻止热量向外层空间释放。
prevent…from doing 防止/阻止…发生We must prevent the news from spreading. 我们应该阻止这个消息的传播。
Nothing can prevent him from going away. 什么也不能阻止他离开。
特别提示：(1)这个句型中prevent还可以被stop或keep替代。
(2)主动句中，prevent和stop后面的from可以省略，keep后的from不能省略；被动句中三个词后的from都不能省略。
联想扩展：prevent vt. 防止；预防；阻止（1）跟名词或代词Man is finding ways to prevent natural disasters. 人类正在寻找预防自然灾害的办法。
Vitamin C is supposed to prevent colds. 据认为维生素C能预防感冒。
（2）跟动名词Teachers now have no ways to prevent students’ listening to MP3 in class.老师们现在没办法阻止学生们上课听MP3。
H1N1 flu prevented his coming to school. 甲流使他不能来上课。
（3）prevention n.预防；防止（4）preventive adj. 预防性的即时活用：1、We should do what we can to ______ the Changjiang River______.A. stop; from pollutingB. keep; from being pollutedC. prevent; from pollutingD. keep; being polluting2、Nobody can stop the naughty boy ______.A. from punishing B. being punishing C. from being punished D. to be punished3、The heavy rain ______ us starting out on time. A. kept B. prevented C. protected D. was stopped4、It seems very difficult _________.A. to stop the child to cryB. restraining the child to cryC. to keep the child from cryingD. holding the child’s cr ying答案：B C BC8、So whether life will continue on the earth for millions of years to come will depend on whether this problem can be solved. 所以，在未来几百万年时间里生命能否在地球上延续取决与这个问题能否得到解决。