The earliest humans did not know how to start a fire, so it is likely that they 9
obtained it through natural events, such as fires caused by lightning, or from forest
保存する
fires. Desperate to save this fire, our ancestors might have tried to preserve it by
setting fire to pieces of wood and then trying to keep them burning continuously.
However, (B)this would not have been effective because early humans rarely stayed
in one place for very long, and any fires they had been using would go out when they
moved from one location to another. Then, probably by chance, one of our early
ancestors discovered that sparks are produced when stones are hit against each other,
and the making of fire was revolutionized.