sentence2_structure: Woolly mammoths<>began<>because of hunting by humans
sentence1: The woolly mammoth went extinct in these parts about 10,000 years ago, but for those of us addicted to the need to search and search again, California frontiers remain as wild and woolly as they were when the first human explorers walked across the Bering straits to a New World.
sentence2: Woolly mammoths began to go extinct thousands of years ago because of hunting by humans.
question: Why did woolly mammoths began to go extinct thousands of years ago?