问题详情

It is not known with any certainty when man first learned how to make use of fire, but when he did, his life was changed in many ways. With fire he found he had a means of keeping warm in cold weather, of boiling water, cooking meals and keeping dangerous animals away. Later he found that fire could be used to extract certain metals from ores. Then he made metals become tools, weapons and decorations.
Still later, it was discovered that two metals together could form. a new but strong metal. Thus the science of preparing metal for use began, although it happened more by chance than by any planned purpose on the part of those who were concerned about it.
When was man"s life changed in many ways？
A．When he did.
B．It is not known.
C．When he learned how to make use of fire.
D．With fire.请帮忙给出正确答案和分析，谢谢！