【正确答案】
A
【答案解析】[听力原文]19-21
M: Doctor Thomas? This is Keith Bradley from The Daily News. I'd like to ask you some questions about the new official standard weight that you purchased.
W: I'd be happy to help you. What would you like to know?
M: First of all, how is the standard weight used?
W: Well, the people in our department use it to check the scales all over the country. The Department of Weights and Measures—we're a government agency—it's our responsibility to see that all the scales measure a kilogram accurately. So this is the weight we use to adjust the scales.
M: How did you check the scales before?
W: 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 that was too porous—it absorbed too much moisture.
M: Oh, so when the weather was humid, it weighed more. And when it was dry, it weighed less.
W: 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.
M: How much did it cost?
W: About forty-five thousand dollars.
M: Forty-five thousand dollars! For a one kilogram weight! That's more expensive than gold. Is it really worth that much?
W: 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's one standard. Think of the drug industry, for example: those companies rely on high accuracy scales to manufacture and package medicine.
19．What is the conversation mainly about?
[解析] 选项都是一些总结性的词句表明该题可能就对话的主旨或大意提问。由对话开头就提到的some questions about the new official standard weight that you purchased可判断该对话是围绕“新的标准测重砝码”展开的，故选[A]。[D]和[C]都是针对对话中it was made of poor quality metal that was too porous—it absorbed too much moisture没的干扰项。[D]在对话中没有涉及。