The world is getting smaller, at least when it comes to language. More and more people speak the three most common languages: English, Spanish, and Mandarin. As a result, local languages are being forgotten. In many parts of the world, grandparents speak a language their grandchildren don’t understand. As languages aren't taught to children or spoken at home, these local languages are slowly disappearing.A language is said to be in trouble when less than 30% of children in the community speak it. It is considered a dying language. If children no longer learn to use a language, it will have fewer and fewer speakers over time and, eventually, the language will be gone. Why do we have to keep languages alive? Languages hold the key to understanding a culture's beliefs and values. They show how a culture understands or explains the world. "You need to look at a variety of languages, because no one language can express everything," said Dr. Linda Cumberland who is working to save Assiniboine, a Native American language.Today, UNESCO lists more than 3,000 languages that may disappear by the end of this century. Some of the languages still have a few million speakers and may survive. Unfortunately, hundreds of others have fewer than 25 speakers remaining and may soon be lost forever. What does ‘the key’ in paragraph 2 mean? A.a tool to open a door B.a list of answers to the questions in a test C.the best or only way to achieve something D.the signs used in a map