A、Nothing but conjecture. B、Studying hard. C、Facts, D、Wisdom. C文中听到：He always tried to add more and more facts，后面听到：He filled hi

Darwin was a great scientist. He studied living things in the world.
    He said, "There are thousands of living things. But in the past, the number was smaller. In the far past, a still smaller number. In the beginning perhaps only one."
    Darwin waited a long time before he put these things in to a book. He always tried to add more and more facts: he wanted his ideas about evolution to be right.
    It took him many years to write the book. On the first day, people bought every copy. The men of the churches fought against Darwin’s ideas. His story of the world was different from theirs. So either Darwin or the men of the churches must be wrong. But the churches did not bring any new frets, or better ideas. They only brought angry words.
    Later, Darwin wrote a book about the evolution of man. He said that man is also a kind of animal. And again, Dar win did not just write down his own ideas. He filled his book with facts. We know now that he was right. There have been men for more than a million years. We have found some of their bones. Bones have told us a lot about the evolution of living things.
    Like any other animals, man slowly changed through time. But we cannot find the bones of man from a few mil lion years ago. There were not any men at that time. The world’s animals were different then.
    But the bones can take us backwards through time into the past. And they can help us with our study of the evolution of life.