The correct answer is D.
This was the first manner in which humans adapted to food scarcity, by migrating to new zones and being nomadic, in the constant seek for new lands where they could hunt, fish or collect food.
Later on, they would develop weapons and tools to help them reachs their 'preys' more easily or increase the quantity obtained. The establishment of the first crops meant the transition from the Paleolitic to the Neolitic era, in which human groups started to settle down in a certain territory, to end their nomadic way of life and to substitute it for conducting agricultural and animal husbandry activities.
Hence the options stated described a whole process, but the earliest of all the mechanisms listed was the one detailed in letter D.
