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在空间直角坐标系中，方程x+z2=z的图形是
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Robert Hoss discovers that over 80 percent of people dream in color, but only 25 percent of them are able to remember the color the following morning.
M: I'd be happy to help you. What would you like to know？
W: First of all, how was the standard weight used？
M: Well, the people in our department use it to check the scales all over the country. The department of weights and measures, we are a government agency. It's our responsibility to see that all the scales measure a kilogram accurately so this is the way we use to adjust the scales.
W: How did you check the scales before？
M: We have an old standard weight that we used to use. It had to be replaced because it was imprecise. You see it was made of poor quality metal. It absorbed too much moisture.
W: Oh. So when the weather was humid it weighed more and when it was dry it weighed less.
M: Exactly. And that variation can affect the standards of the whole country. So our department had the new weight made out of higher quality metal.
W: How much did it cost？
M: About 45,000 dollars.
W: 45,000 dollars？ For a one-kilogram weight？ That's more expensive than gold. Is it really worth that much？
M: I'm sure it is. Industries depend on our government agency to monitor the accuracy of scales so that when they buy and sell their products there is one standard. Think of the drag industry, fur example, these companies rely on high accuracy scales to manufacture and package medicine.
What is the main subject of the conversation？
(23)
【C11】
听力原文：W: Well, where did you think the theater director would be？
M: You mean Emily Thompson？ She was away attending a conference.
Q: What does the man imply？
(16)
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