Around 12,000 Years Ago, a Sudden Extinction Occurred on the Temperate

Around 12,000 years ago, a sudden extinction occurred on the temperate grasslands of North America, during which most of the diverse large mammal species died out. A corresponding extinction did not occur on the African savanna, also a temperate grassland, and today it still has diverse herds of large mammals. What possible, but controversial, explanation is thought by some people to explain the North American extinction?

A) Declining habitat or food supply due to climate change
B) Arrival of humans in North America
C) Receding ice sheets, leading to a climate too warm to support megafauna
D) Expanding ice sheets, leading to a climate too cold to support megafauna