C
We often talk about global warming. Do you know how global warming happens? This experiment helps you learn how a greenhouse works, and how greenhouse gases influence the earth’s atmosphere.
What you need:
Two thermometers (温度计)
A notebook
A pencil or pen
A clear bottle
A watch or clock
A sunny area
What you do:
1. Put the thermometers in direct sunlight. Let them sit in the sun for three minutes.
2. Draw two columns (栏), “Thermometer A” and “Thermometer B”, in the notebook.
3. After three minutes, read and record the time and temperatures in the notebook.
4. Place one of the thermometers in the bottle and close it.
5. Record the temperatures of the thermometers every ten minutes.
6. Discuss how the bottle influences the temperature.
What’s going on?
The temperature outside the bottle is changing, as the warm air mixes with the passing cooler air. The air inside the bottle can’t mix with the air outside — it just gets warmer as the sunlight heats it up. A greenhouse works in a similar way: sunlight creates heat that can’t get out of the glass.

47. What do you need in the experiment?
A. A dark room. B. A paper box. C. Some water. D. Two thermometers.
48. How often do you record the temperatures of the thermometers?
A. Every five minutes. B. Every ten minutes. C. Every fifteen minutes. D. Every twenty minutes.
49. Why does the air in the bottle get warmer as the sunlight heats it up?
A. Because it can’t stay in the glass. B. Because it can’t get much sunlight. C. Because it can’t mix with the air outside. D. Because it can’t influence the temperature.
50. What can you learn from the experiment?
A. When the glass breaks. B. Why the sunlight is helpful. C. How a greenhouse works. D. How the temperature changes.

47~50 DBCC