Before going outside in the morning,many of us check a window thermometer(温度计)for the temperature.Th

题目

Before going outside in the morning,many of us check a window thermometer(温度计)for the temperature.This helps us decide what to wear.71 .We want our food to be a certain coldness in the refrigerator.We want it a certain hotness in the oven(烤箱).If we don’t feel well,we use a thermometer to see if we have a fever.We keep our rooms a certain warmth in the winter and a certain coolness in the summer.
Not all the thermometers use the same system to measure temperature.We use a system called the Fahrenheit scale.But most other countries use the Centigrade scale.
Both systems use the freezing and boiling points of water as their guide.72 .
The most common kind of thermometer is made with mercury(水银)inside a clear glass tube.As mercury (or any other liquid ) becomes hot,it expands.As it gets colder,it contracts(收缩).That is why on hot days the mercury line is high in the glass tube.73 _.
First,take a clear glass juice bottle that has a cap; fill the bottle with coloured water.Tap

答案

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