Fill in each of the 15 blanks in the passage with the most likely answer.
Prehistoric people are human beings who lived before writing was invented about 5,500 years ago. Writing 1 people to record information they wished to save, 2 descriptions of s in their lives. 3 this way, the invention of writing marked the beginning of history. The period before human beings learned to write is called prehistory.
Scientists first discovered evidence of prehistoric people in the mid-1800’s. Most of this evidence 4 ancient, sharp-edged stone tools and fossilized (已变成化石的) bones of prehistoric people. 5 scientists collected more fossils of prehistoric people, they began to form a clearer 6 of what these early people looked like. For example, scientists learned that early human beings had smaller brains than most modern men and women have. This evidence indicated 7 humans had evolved—that is, modified their physical structure over time. Scientists developed a set of ideas about human origins 8 the theory of human evolution. This theory states that as the 9 of the prehistoric world changed, our prehistoric ancestors went 10 a series of changes that resulted in the first human beings. They, 11 , evolved into modern human beings. Evidence of prehistoric people is 12 and difficult to find. Scientists must 13 their theory on this extremely limited evidence. As a result, scientists cannot 14 present a detailed picture of early human life. 15 , new discoveries sometimes disprove theories that scientists already hold. Fill in each of the 15 blanks in the passage with the most likely answer.