缺点：不仅消耗大量电能，留下残余物，如果控制不好，还会产生有毒物质，造成二次污染。
14、在显微镜下观察物体有一定的要求。物体必须制成玻片标本，才能在显微镜下观察它的精细结构。
年，英国科学家罗伯特。胡克用自制的复合显微镜观察一块软木薄片的结构，发现它们看上去像一间间长方形的小房间，就把它命名为细胞。
5、铁生锈变成了铁锈，这是一种化学变化。水分和氧气是使铁生锈的原因。
11、显微镜的发明，是人类认识世界的一大飞跃，把有类带入了一个崭新的微观世界。为了看到更小的物体，人们又研制出了电子显微镜和扫描隧道显微镜。电子显微镜可把物体放大到200万倍。
答：说明米饭不是甜的，但米饭含有淀粉，在我们咀嚼的过程中发生了变化，变得有甜味了。
二、问答：5、垃圾的**利用有哪些好处？
2、你知道日食的形成过程吗？
20、在观星过程中，我们看到的天空中有一条闪亮的“银河”光带，实际是由许许多多的恒星组成的一个恒星集团，被人们称为银河系。我们生活的地球在银河系。unit6 an old man tried to move the mountains.
一、语法难点。
本单元的语法重点是状语从句，主要讲述以下三种状语从句。
引导条件状语从句
unless = if … not “除非，若不”
they will go tomorrow unless it rains.= they will go tomorrow if it doesn’t rains.
2. as soon as引导时间状语从句。 “一……就” he will come and see you as soon as he can.
3. so...that引导结果状语从句。
句型1“主语+谓语+so+形容词/副词+that从句”
the wind was so strong that we could hardly move forward.
句型2： so +形容词 + a/an + 单数名词 + that从句。
it was so hot a day that they all went swimming.
句型3. so + many/ few + 复数名词 + that从句。
he has so few friends that he often feels lonely.
句型4： so +much/ little + 不可数名词 + that 从句。
i had so little money that i couldn’t buy a pen.
二、重点短语及词组。
1. work on doing sth. 致力于做某 2. assoon as ..一……就…..3. once upon a time 从前。
4. continue to do sth. 继续做某事 5. make sth. happen 使某事发生 to do sth. 试图做某事。
7. the journey to sp. .
之旅8. tell the/a story 讲故事9. put on 穿上10.
a little bit 有点儿。
11. keep doing sth. 坚持做某事12. give up 放弃13. instead of 代替；反而。
14. turn ..into 变成15. get married 结婚16. the main character 主要人物；主人公。
17. at other times 在另外一些时候18. be able to 能；会19. come out (书、电影等)出版。
20. become interested in. 对……感兴趣21. walk to the other side 走到另一边去。
22. a fairy tale 一个神话故事23. the rest of the story 故事的其余部分。
24. le**e sb. to do sth. 让某人做某事25. make a plan to do sth. 筹划/计划做某事。
26. go to sleep 去睡觉27. lead sb. to sp. 把某人领到某地28. get lost 迷路。
29. change one’s plan 改变计划30. tell sb. to do sth. 叫某人做某事。
31. in the moonlight 在月光下32. find one’ s way home 找到某人回家的路。
33. the next day 第二天34. send sb. to sp. 派某人去某地35. so...that 如此… …以至于…
三．知识点讲解。
section a
1. how does the story begin? 故事是怎么发生的？
解析】begin → began → begun v 开始 → beginning n 开始 at the beginning of 在……开始。
拓展】begin to do sth/ doing sth 开始做某事。
2. a man told yu gong that he could never do it.【解析1】tell sb. that 告诉某人。
辨析】speak/talk/say/tell
say“讲，说”，强调说话内容。
sayitinchineseplease． hesaysthathesawthemanyesterday．
say+ 说话内容。
say to sb.
it is said that...据说”。 it is said that he could stay under the water for a long time.
speak vt，“说”“讲”，其宾语常是某种语言。speakfrench说法语；
speak+ 语言。
speak to sb. may i speak to tom?
talk“讲、谈论，谈话”是不及物动词，talk to/ with sb. about sth. (1)talk about/of 谈论…… 2)talk to / with 和…交谈。
give a talk做报告 （talk n.报告） h**e a talk听报告。
tell“告诉，对…说”.作及物动词，
tell the truth 说真话 tell a lie说谎 tell the time “报时“ tellastory讲故事。
tell me a story
tell : 辨别，说出区别 tell a from b
tell the differences between a and b
练习一：1. did he __it in english? a. tell b. speak c. say d. talk
2. the teacher __us to finish the homework in time. a.
tells b. speaks c. says d.
talks
would you like to __us about you hometown. a. speak b. talk c. say d. tell
the radio __that there will be another he**y rain in guangdong.
too bad. it has rained for the whole week.
a. tells b. talks c. says d. speaks
i always tell my students __on the road because it’s really dangerous.
a. not to play b. to play not c. not playing d. not play
a man saw yu gong and his (children/family) when they were working on moving the mountains.
解析】work on 忙于； 从事。
2011湖南邵阳】— could i borrow your computer, bob?
sorry, i am __taking out b. turning on c. working on
拓展】work 短语总结：
) the builders are working __building a great building although it’s so hot today.
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