四级练习2011.12.26
[audio]http://sound.yywz123.com/tingbbs/cet4/cet420111226.mp3[/audio]M: Want to go out and get something to eat?
W: I can't.I have a chemistry midterm on Monday and a German exam on Tuesday.
M: I have a geology exam Monday myself,but I think I'm ready for it.
W: What kind of exam is it going to be multiple choice or essay?
M: Neither.The professor is going to give us a mineral sample and we have to identify it.
W: How do you do that? I mean,a rock's a rock,isn't it?
M: Actually,there are a lot of tests you can perform on minerals to help you figure out what they are.Probably the first tests I'll do are scratch tests.(1)_______________________.That tells you the relative hardness of the sample.
W: What other tests will you do?
M: I'll probably do a streak test next.In that test,you rub an unknown mineral against a piece of china to see what color the streak is.
W: Why can't you just look at the mineral to see what color it is?
M: (2)_______________________.But a streak test shows the mineral's true color. Then there's always the specific gravity test,the blowpipe test...oh,and...
W: And after you've done all these tests,can you positively identify any mineral?
M: Well, usually...but not always.I just hope I can on Monday!
**** Hidden Message ***** 1.when you do a scratch test,you rub the sample on a know mineral,and to see if the unknow mineral scratch the know mineral,for viceversa.
2.well,you can,but sometimes the mineral have some other substance in it
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