The first two stages in the development of civilized1 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.

• 在人类文明发展的进程中，最初的两个阶段可能是简单的武器的发明和火的发现，尽管没有人确切地知道人是在什么时候掌握火的使用的。