Passage Five At some time around 2300BC, give or take a century or two, a large number of the major civilizations of the world collapsed, in Mesopotamia, Egypt, Israel, Anatolia, and Greece, as well as in Afghanistan and China. All of them the first urban civilizations fell into rain at more or less the same time. A thousand years later, around 1200BC, many of the civilizations of the same regions again collapsed at about the same time. The reasons for these widespread and apparently simultaneous disasters which coincided with changes to cultures and societies elsewhere, such as in Britain, have long been a fascinating mystery. Traditional explanations included warfare, famine, and more recently systems collapse, but the apparent absence of direct archaeological or written evidence for causes, as opposed to effects, has led many archaeologists and historians into a resigned assumption that no definite explanation can be found. Over the past 15 years, however, a new type of ’natural disaster’ has been proffered which is beginning to be regarded by many scholars as the most probable single explanation for widespread and simultaneous cultural collapse. The new theory has been advanced largely by astronomers and remains largely unknown by archaeologists (notable exceptions include Professor Baillie of Belfast and Dr. Euan Mackie in Glasgow). The theory postulates that the disasters were caused by the impact of comets or other types of cosmic debris on the Earth. French archaeologist Chude Schaeffer, in 1948, published his analysis and compared the destruction layers of more than 40 archaeological sites. He was the first scholar to detect that all of the sites had been totally destroyed several times in the Early, Middle and Late Bronze Age, apparently simultaneously. Since the damage did not show signs of military or other human involvement, and, in any case, was too excessive, he argued that repeated seismic activity might have been responsible. Schaeffer was not taken seriously in 1948, but since then natural scientists have found widespread and unambiguous evidence for abrupt climate change, sudden sea level changes, catastrophic inundations, and seismic activity at several periods since the last Ice Age, particularly around 2300BC. Areas such as the Sahara, which were once farmed, became deserts. Tree rings show disastrous conditions at 2350BC. In Mesopotamia the land appears to have been inundated, devastated, or totally burned. Scholars who, following Schaeffer, favor earthquakes as the principal cause of civilization collapse, argue that the world can expect earthquakes every 1000 ～2000 years, leading to abandonment of sites; while scholars who prefer climate change as the principal cause argue that severe droughts caused agriculture to fail and that .societies inexorably fell apart as a result. The question remained what caused the climate change or the earthquakes. By the late 1970’s British astronomers Clube and Napier of Oxford University had begun to investigate cometary impact as the ultimate cause. In 1980, the Nobel prize-winning chemist Luis Alvarez and his colleagues published their paper arguing that a cosmic impact had caused the extinction of the dinosaurs. He showed that large amounts of iridium found in geological layers from the time of the dinosaurs had a cosmic origin. Alvarez’s paper stimulated further research by Clube and Napier, Professor Mark Bailey, Duncan Steel and Sir Fred Hoyle. All now support the theory of cometary impact and what is now known as the British School of Coherent Catastrophism. The collapse of civilizations has remained a fascinating mystery because ______.

A. it occurred simultaneously.
B. it occurred at a time similar to noticeable cultural and social changes
C. there are no written records.
D. all of the above.