[单项选择]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, somehow invented certain sounds to express thoughts and feelings, actions, and things, so that they could communicate with each other; and that later they agreed upon certain signs, called letters, which could be combined to represent those sounds, and which could be written down, these sounds, whether spoken or written in letters we call words. The power of words, then, lies in their associations -- the things they bring up before our minds. Words become filled with meanings for us by experience. And the longer we live, the more certain words recall to us the glad and sad events of our past; and the more we read and learn, the more the number of words that mean something to us increases. Great writers are those who not only have great thoughts but also express these thoughts in words which appeal powerfully to our minds and emotions. Th