As civil wars erupted throughout the Roman Republic in the 1st century B. C., country dwellers may have fled to cities. Before they left, some people buried their valuables to hide them from armies. Now social scientists have studied these coin stores to answer a long-standing Roman mystery.Historians have long debated Rome’s population size during the 1st century B.C. Starting in 28 B. C., censuses (人口普查) conducted under tile first Roman emperor showed the population at about 5 million--a 10-fold increase over that of the Roman Republic a century earlier. About a third of this jump can be explained by the extension of citizenship to Roman allies across Italy. But where did the rest of the people come from Some historians say the answer is simply population explosion. Others argue that the empire included women and children in its census, whereas the republic only counted adult males.To settle the debate, social scientist Peter Turchin and his colleague Walter Scheidel turned to coin stores. Amateur antiquities hunters armed with metal detectors have found hundreds of clay pots filled with silver coins, called denarii (古罗马便士), throughout Italy dating back to the Roman Empire. Turchin says these buried treasures can be used as a signal for times of social instability. People would hide their money during dangerous times, and if they were killed or displaced by war, they never took their treasure.Turchin and Scheidel combined numbers of coin stores from 250 B.C. to 100 B.C. with data from the Roman Republic censuses to check the relationship between them. For example, population dropped during the Second Punic War (布匿战争), and that coincides with a jump in coin stores dated to that time. Then, from data on coins stored from 100 B.C. to 50 C. E., the researchers inferred population during that era. The range predicted by the coin store model is about half that of the high estimate, indicating that civil wars reduced about 100 000 people, the researchers report online today. "We know this period was extremely violent with internal warfare across Italy," says Turchin. In all. the findings strengthen the hypothesis that the Augustan censuses were not confined to adult men."This paper has the great virtue of pushing the debate back toward actual evidence," says historian Ian Morris of Stanford University. But historian J. Geoffrey Kron of the University of Victoria in Canada, a proponent of the population explosion hypothesis, believes that it’s a stretch to connect increased coin storing with more deaths and that some people may have hid money from political opponents. He points out that one of the 1st century B.C. coin-store peaks coincides with a civil war that didn’t cause high casualties. "Increased coin stores only represent evidence of fears of violence," Kron says. "These fears may or may not have been justified by actual events.\ According to Peter Turchin and Walter Scheide, which shall be relied on to solve the dispute（）

A) Amateur antiquities hunters.
B) metal detectors.
C) clay pots.
D) silver coins.