The correct answer is A.
The Paleolithic era comprised the 99% of human history. It started 2.5 million years ago until 4,000 AC. During its later stage, the Upper Paleolithic, humans were able to develop higher quality tools, using strategies like the ones commented in the question: chipping flint pebbles into blades and scrapers that had sharp edges.
These improvements gave rise to an important technical revolution and important productivity improvements, which triggered the development of two new economic activities: agriculture and animal husbandry. When these new activities appeared the Paleolithic was finished and a new period started, the Neolithic.
