The first two stages in the development of civilized man were probably the invention of primitive weapons and the discovery of fire, although nobody knows exactly when he acquired the use of the latter. The 【C1】______ of language is also obscure (模糊). No doubt it began very. 【C2】______ . Animals have a few 【C3】______ that 'serve as signals, 【C4】______ even the highest apes have not been found able to 【C5】______ words, even with the most 【C6】______ professional instruction. The 【C7】______ brain of man is apparently a necessity for the 【C8】______ of speech. When man became 【C9】______ intel-ligent, we must 【C10】______ that he gradually 【C11】______ the number of cries for different purposes. It was a great day 【C12】______ he 【C13】______ that speech could be used for narrative. I am 【C14】______ to think that language has been the most important single 【C15】______ in the development of man. Two important 【C16】______ came not so long before the dawn of written history. The first was the domestication(家庭驯养) of animals the second was agriculture. Agriculture made possible an immense increase in the number of the human 【C17】______ in the regions where it could be successfully practiced. Another fundamental technical 【C18】______ was writing, which, like spoken language, developed out of pictures, but as soon as it had reached a certain stage, it was possible to keep records and 【C19】______ information to people who were not 【C20】______ when the information was given. 【C1】