sentence2_structure: Woolly mammoths<>began<>because of hunting by humans
sentence1: In 1993, the team uncovered the bones of extinct creatures like woolly mammoth, along with human tools, from a 40,000 year old site in northern China.
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?