Read this short passage and answer the question below:

Excerpt from Stuff Matters
By Mark Miodownik

At some point humans made the discovery that would end the Stone Age and open the door to a seemingly unlimited supply of the stuff. They discovered that a certain greenish rock, when put into a very hot fire and surrounded by red-hot embers, turns into a shiny piece of metal. This greenish rock was malachite, and the metal was, of course, copper. It must have been the most dazzling revelation. Suddenly the discoverers were surrounded not by dead inert rock but by mysterious stuff that had an inner life. They would have been capable of performing this transformation with only a few particular types of rock, such as malachite, because getting it to work reliably depends not just on identifying these rocks but also on carefully controlling the chemical conditions of the fire. But they must have suspected that those rocks that didn’t work, that remained obstinately rock-like however hot the fire became, had hidden secrets. They were right. It’s a process that works for many minerals, although it would be thousands of years before an understanding of the chemistry required (controlling the chemical reactions between the rock and the gases created in the fire) led to the next real breakthrough in smelting. In the meantime, from around 5000 BC, early metal smiths used trial and error to hone the process of the production of copper. The making of copper tools initiated a spectacular growth in human technology, being instrumental in the birth of other technologies, cities, and the first great civilizations. The pyramids of Egypt are an example of what became possible once there were plentiful copper tools. Each block of stone in each pyramid was extracted from amine and individually hand-carved using copper chisels. It is estimated that ten thousand tons of copper ore were mined throughout ancient Egypt to create the three hundred thousand chisels needed. It was an enormous achievement, without which the pyramids could not have been built, however many slaves were used, since it is not practical to carve rock without metal tools. It is all the more impressive given that copper is not the ideal material for cutting rock since it is not very hard. Sculpting a piece of limestone with a copper chisel quickly blunts the chisel. It is estimated that the copper chisels would have needed to be sharpened every few hammer blows in order for them to be useful.
What is the author’s main message? A) Copper was the first metal used by humans.
B) Copper was a critical tool in building the pyramids.
C) Humans were not able to effectively use copper at first.
D) The discovery of copper was the beginning of civilizations.