다음 글의 밑줄 친 부분 중, 문맥상 낱말의 쓰임이 적절하지 않은 것은?
Scientists have come up with a new theory on why woolly mammoths became ① extinct 21,000 years ago. Up until now, people have believed that mammoths, the 3-metre-high relatives of elephants, died out because they were hunted to extinction. New research shows they ② ran out of grass, and that was caused by global warming 21 millennia ago. Researchers from the UK’s Durham University suggest the hairy dinosaurs ③ starved to death because forests took over the grasslands they needed to survive. As the Earth became warmer and wetter, forests ④ dwindled and the mammoth had ⑤ fewer areas to graze. “Mammoths had roamed and munched their way across many parts of Europe,” said lead researcher Professor Brian Huntley.
*woolly mammoth: 털매머드