Researchers from the University of Colorado at Boulder examined stone tools dating from the Middle stone Age, some 75, 000 years ago, from Blombos Cave in what is now South Africa.
When a stone falls into a pond, the ripples persist for a while. The credit crunch was a whopping great boulder.
一块石头掉落水池所引起的波澜，会持续好长一段时间。而信贷危机就是这样一块特别大的石头。
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Nowadays such heavy belts for outdoor transporting of bulk materials like stone, coal or boulder, are rugged rubber belts with a steel cord traction member.