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a big glass jar
a candleholder
a shallow dish with water
a match
2. How do we do the experiment?
Please watch carefully as a student does this experiment.
1.Put the candle in the candleholder.
2.Put the candleholder in the dish.
3.Fill the dish half full with water.
4.Light the candle. Let the candle burn for two or three minutes.
5.Put the jar over the dish until the top of the jar rests on the dish.
What is happening?
1. The candle stops burning.
Because the candle burns, it uses up oxygen in the jar.
Why?
2.The water inside the jar goes up and fills about one fifth of the jar.
Why?
Because about one fifth of the air is made up of oxygen.
Read the text silently and finish Ex. 1
Important phrases:
1.use up :用完，用光。
2.keep sb/sth doing:让某人不停的做某事。
3.let sb do sth:让某人做某事。
4. stop doing sth:停止做某事。
5. fill sth with sth:充满，装满
分数的表达法：
口 诀:
分子基，分母序。分子﹥1 ，分母加s 。
三分之一：one third.
三分之二：two thirds.