They don't know or care about how the TV works or what components exist inside, only that they can interact with it via its inputs (remote control, power plug, etc.) and outputs (screen and speakers).

他们不知道也不关心电视是如何工作的、里面都存在那些组成要素，他们所做的只是通过输入（遥控器、电源等）和输出（屏幕和扬声器）来同电视进行互动。

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Singletons are a useful way to control access to a class, making sure that only one instance can exist.

单例模式是一种有用的控制类访问的途径，他能保证只有一个类实例存在。

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Researchers can only question the firms that exist; they cannot talk to all the ones that might exist, if India’s labour laws permitted them to prosper.

研究者只能询问现存的公司，他们不能询问所有可能存在的公司，印度的劳工法是否可以促使公司的繁荣。

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And so there are only two kinds of waves that can exist on this violin string, standing or traveling.

由于这只有两种波,可以存在在这条弦上，驻波或行波。

麻省理工公开课 - 固态化学导论课程节选

It can only exist until the voters discover that they can vote themselves largesse from the public treasury.

FORBES: Peter Schiff on The Crash Still to Come, Foreign Bonds, and How to Fix the US Government

That so long as a state of general unemployment prevails, in the sense that unused resources of all kinds exist, monetary expansion can be only beneficial, few people will deny.

FORBES: Hayek: "General Unemployment" Requires Easy Money

Even if products are getting cheaper and consumers are happy, a trustbuster needs to make sure that industries which currently exist only in laboratories and geeks' heads can break into the market.

ECONOMIST: Beleaguered Microsoft