国家对医疗器械实行分类管理，人工心脏瓣膜在管理分类上属于（）

A．They circle helplessly.B．They fly by radar.C．They use landmarks.D．They use the moon. 点击查看答案

听力原文： There are over 3,000 languages that are used throughout the world today. Almost all of these languages belong to a much smaller number of language families. All of the languages within a language family are related and all of them have a similar history. Therefore, the grammar, vocabulary, and sounds of related languages ate similar. In addition, the way of thinking and the style. of talking among related languages is similar. Even though there are over 3,000 languages that are used today, there are only 20 or 30 major language families. Each of these large families includes many individual languages. The language that we are using now is English and English is, of course, a member of a larger language family. English is a member of the Indo-European language family. The Indo-European language family includes most of the languages that are spoken throughout Europe, languages such as English, French, and Greek. Of course, nowadays many Indo-European languages are spoken in other parts of the world. For instance, Spanish, which is an Indo-European language, is spoken throughout South and Central America, but originally it was spoken only in Europe.(30)A．About 4,000.B．Over 300.C．Less than 2,000.D．Over 3,000. 点击查看答案