六级练习2015.01.13
[audio]http://sound.yywz123.com/tingbbs/cet6/cet620150113.mp3[/audio]We all scream for water when thirsty, but do you know in very hot, dry weather, (1)___________________—as if they are crying out for help?
You see, in a plant’s stem there are hundreds of “water pipes” that bring water and minerals from the soil all the way up to the leaves. (2)___________________, it becomes harder and harder for the plants to do this.
In severe droughts, plants have to fight to pull out any water available. Scientist Robert winter has found out that when it is really bad their water pipes snap from the tension like rubber bands. When that happens, (3)__________________. The snapping pipes make noises ten thousand times more quiet than a whisper.
**** Hidden Message ***** plants also make same sounds
as ground turns dry
the whole plant * a little
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