单选题 How men first learned to invent words is unknown; in other words, the origin of language is a mystery. All we really know is that men, unlike animals, invented certain sounds to express thoughts and feelings, actions and things, so that they could communicate with each other, and later they agreed on certain signs. These signs were called letters, which could be combined to represent those sounds and could be written down. Those sounds, whether spoken or written in letters, are called words. The power of words, then, exists in their associations—the things they bring up before our minds. Words become filled with meaning for us by experience, and the longer we live, the more certain words remind us of the glad and sad events of our past, and the more we read and learn, the more number of words increases. Great writers are those who not only have great thoughts but also express these thoughts in words which deeply attract our minds and emotions. This skillful use of words is called "literary style". Above all, a real poet can express his meaning in words which sing like music and can move men to tears. We should, therefore, learn to choose our words carefully and use them properly, or they will make our speech silly and vulgar.