In the 1930s, a British scholar predicted that there would be a serious shortage of copper resources around the world based on the results of his own research. The current situation is that the U. S. Geological Survey has estimated that the copper resources on the earth's surface can be at least It reaches 3 billion tons and is available for human use for 185,000 years. With the improvement of human exploration technology, this number may continue to rise in the future. The most appropriate headline for this text is:. ['Technology can only be improved by constantly correcting mistakes.', "Earth's copper resources are far from exhausted.", 'The shortage of copper resources has been resolved.', 'Authoritative scholars also make big mistakes.']