Answer:
D). Ate a varied diet of plants and meat.
Step-by-step explanation:
Pre-historic hunter-gatherers 'ate a varied diet of plants and meat' as they were dependent on plenty of sources for obtaining their food. They obtained their food by pursuing various activities like 'hunting, gathering/collecting wild herbs and edibles, scavenging, fishing, etc.' Their sole dependence on the abundance of nature made them eat various sources of food until the advent of agriculture 12k years ago. Thus, option D is the correct answer.