Using the points and examples from the talk,
请用对话中提到的观点和例子
explain how substitute goods and complement goods influence demand for a particular product.
解释替代品和互补品是如何影响某种特有产品的需求的。
Listen to part of a lecture in an economics class.
请听经济学课上的部分内容。

So, when we talked about the demand for a product,
当我们谈到某一产品的需求时，
we're referring to how much consumers want to buy it, right?
我们指的是有多少消费者想要购买这种产品，对吧？
And often the demand for a product is influenced by its price,
一种产品的需求量经常受到其价格的影响，
the more expensive it becomes the less chance people want to buy it.
产品越贵，人们想要购买它的几率就越小。
OK, but that's not the whole story.
不过...这还没完。
Sometimes the demand for a product can also be influenced by the price of other related products.
有时产品的需求量也会受到其他相关产品的价格的影响。
First, there are other products called “substitute goods”.
首先，有些其他产品被称为“替代品”。
If products can be substituted for one another then, um, well, then they are called substitute goods.
如果某些产品可以替代另一种产品，那么，它们就被称为替代品。
They are similar enough to be interchangeable.
它们彼此相似到足以互相替代。
And, uh, the increase of price of one means the increase for the demand of the other.
而一种产品价格的上涨则意味着其他产品需求的增加。
Like, uh, like butter and margarine.
就像......就像黄油和人造黄油一样。
They are pretty much used for the same purposes.
它们基本上都用于同样的用途。
Margarine is butter's substitute and you can bake equally well with either.
人造黄油是黄油的替代品，不管用哪个都同样可以做好烘焙。
Well, when the price of butter goes up, it becomes less affordable, and so what do people do?
所以，当黄油的价格上涨，不再那么容易买得起的时候，人们会做些什么呢？
They buy margarine instead, right?
他们会选择购买人造黄油，对吗？
So, uh, you see, increase of the price of butter increases the demand for margarine.
所以，你看，黄油价格的上涨使得人造黄油的需求有所增加。
Now, another instance with the price of one product can influence the demand of another is,
那么，关于一种产品的价格可以影响另一种产品的需求的另一个例子就是：
uh, is when you have two products that can't be used without each other.
两种产品在使用时缺一不可的情况。
Those products we call “complement goods”.
我们称这些产品为“互补品”。
They complement, or complete, each other, if you will.
它们互相补充，或者互相完善。
Like compact disks and compact disk players.
就像光盘和光盘播放器一样。
You need both products in order to use either.
要使用其中之一，你需要同时拥有这两种产品。
So if the price of either product increases demand for both is likely to decrease.
所以如果其中一种产品的价格上涨，那么两者的需求量都有可能下降。
And if the price of the CDs goes up, well, demand for them will go down, right?
比如，当光盘的价格上涨时，它的需求会有所下降，对吗？
And because CD's and CD player compliment each other,
而由于光盘和光盘播放器互为补充，
what will also happen is that the demand for CD player will go down, too.
光盘播放器的需求也会随之下降。