Final answer:
Segment D, 'People made advances that allowed them to adapt to new environments,' best describes life in the Mesolithic Era, representing a time of technological and social advancements that allowed hunter-gatherers to adapt to various environments and eventually led to the agricultural revolution of the Neolithic Age.
Step-by-step explanation:
During the Mesolithic Era, humans continued their hunter-gatherer lifestyle but also made significant technological and social advances, which allowed them to adapt and thrive in a variety of environments. Hunting and gathering were still the primary means of subsistence, and while groups would settle in an area with abundant resources, they did not stay in one place for very long periods due to the need to follow seasonal migrations of game or to find new sources of food as resources diminished.
The Mesolithic Era, often referred to as the middle Stone Age, was a period of transition between the Paleolithic hunter-gatherer society and the agricultural focus of the Neolithic Age. Changes in stone tool technologies, increased reliance on fish and wild plants, and the development of small, more permanent settlements occurred during this time. This era allowed for adaptations to the environment that paved the way for the growth of agriculture and sedentary life, thus setting the stage for the Neolithic Revolution.