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外语
A、They are never effective. B、They are simple to perform. C、They are not always very easy. D、They are usually valid. BWhat does
A、They are never effective. B、They are simple to perform. C、They are not always very easy. D、They are usually valid. BWhat does
admin
2013-06-17
32
问题
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. When you do a scratch test, you rub the sample on a known mineral to see if the unknown mineral scratches the known mineral or vice versa. 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: Well, you can, but sometimes a mineral has some other substance in it, and the substance can change its color. 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, you can positively identify any mineral?
M: Well, usually...but not always. I just hope I can on Monday!
选项
A、They are never effective.
B、They are simple to perform.
C、They are not always very easy.
D、They are usually valid.
答案
B
解析
What does the man imply about the tests used to identify minerals?
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0
大学英语四级
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