Read the text and choose the appropriate answer.
The Mayas is a lost civilization which had a highly developed system of government and agriculture. They were also wonderful engineers capable of moving huge blocks of stone for long distances, cutting them into precise shapes and sizes, building temples and pyramids. Although the Mayas knew about the wheel, they never used it. What is more surprising is that they suddenly abandoned many of their cities and built new ones in the jungle. Some time around AD 900 Mayan civilization collapsed. By the year 1200, their capital turned into a desert. There were different hypotheses for their sudden disappearance. All we really know is that when the first Europeans appeared on their coast in 1517, this mysterious culture was only a memory.
According to the passage why did the Mayas suddenly abandon their cities?