Why do people take duality as one of the important design features of human language? Can you tell us what language will be if it has no such design feature?(本题4.0分)

标准答案： Duality makes our language productive. A large number of different units can be formed out of a small number of elements – for instance, tens of thousands of words out of a small set of sounds, around 48 in the case of the English language. And out of the huge number of words, there can be astronomical number of possible sentences and phrases, which in turn can combine to form unlimited number of texts. Most animal communication systems do not have this design feature of human language. If language has no such design feature, then it will be like animal communicational system which will be highly limited. It cannot produce a very large number of sound combinations, e.g. words, which are distinct in meaning.