A． The bones of the fossils.B．The place where they were……

Questions 56 to 60 are based on the following passage. New Findings in Archaeology ●South America and Madagascar were joined 70 million years ago
Picture: Reuters An old croc: The discovery in Brazil of a nearly complete fossilised skeleton of the prehistoric crocodile Ubera-basuchus terrificus, above, supports theories that South America and Madagascar were joined 70 million years ago. ●We’ve all just got 40,000 years older Two skulls found in Africa have been identified as the oldest human remains known to science. The fossilised bones found in 1967 were originally thought to be 130,000 years old. But a re-dating of rock layers near those which yielded the fossils showed they are actually about 195,000 years old—from the time modern humans emerged. The skulls, known as Omo I and II, push back the known presence of Homo sapiens in Africa by 40,000 years. The previous oldest Homo sapiens skulls, dated to between 154,000 and 160,000 years old, were found near a village called Herto in the afar region of eastern Ethiopia. Omo I and II were unearthed by famous palaeontologist Richard Leakey along the Omo River in southern Ethiopia, near the town of Kibish. Omo I’s more modern features led to disagreement among experts over whether they were the same age. The rocks in which they were found show they are, said Australian archaeologist Prof Ian McDougall, who made the discovery. He told scientific journal “Nature”: “Omo I and Omo II are relatively securely dated to 195,000 years old, making them the oldest anatomically modern human fossils yet recovered.” Questions: By which means could the scientists tell the age of fossils they have found

A． The bones of the fossils.
B．The place where they were found.
C．The history of humans.
D．Identifying the rock layers of the fossils.