Answer: The correct answer is- Climate change that led to decrease in the size of grassland, causing extinction of Woolly mammoths eventually.
Climate change have caused woolly mammoths to become less reproductively successful and eventually become extinct at the end of the last ice age.
They were adapted to live in extreme cold weather conditions. But at the end of last ice age, the climatic conditions were changed dramatically, which caused an increase in the temperature ( warmer climate). Due to this, size of grassland habitat was decreased ( as their food resource became depleted), causing the extinction of Woolly mammoths eventually.