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In this task, you're given an article and an answer. Your task is to generate the fill-in-the-blank question for this answer based on the given article. The blanks are always at the end of the question, and can be filled with more than one word or phrase.

Article: No one is sure how the ancient Egyptians built the pyramids near Cairo. But a new study suggests they used a little rock'n'roll. Long-ago builders could have attached wooden poles to the stones and rolled them across the sand, the scientists say. "Technically, I think what they're proposing is possible," physicist Daniel Bonn said. People have long puzzled over how the Egyptians moved such huge rocks. And there's no obvious answer. On average, each of the two million big stones weighed about as much as a large pickup truck. The Egyptians somehow moved the stone blocks to the pyramid site from about one kilometer away. The most popular view is that Egyptian workers slid the blocks along smooth paths. Many scientists suspect wokers first would have put the blocks on sleds . Then they would have dragged them along paths. To make the work easier, workers may have lubricated the paths either with wet clay or with the fat from cattle. Bonn has now tested this idea by building small sleds and dragging heavy objects over sand. Evidence from the sand supports this idea. Researchers found small amounts of fat, as well as a large amount of stone and the remains of paths. However , physicist Joseph West think there might have been a simpler way , who led the new study . West said , "I was inspired while watching a television program showing how sleds might have helped with pyramid construction . I thought , "Why don't they just try rolling the things ? " A square could be turned into a rough sort of wheel by attaching wooden poles to its sides , he realized . That , he notes , should make a block of stone "a lot easier to roll than a square". So he tried _ He and his students tied some poles to each of four sides of a 30-kilogram stone block.That action turned the block into somewhat a wheel.Then they placed the block on the ground. They wrapped one end of a rope around the block and pulled.The researchers found they could easily roll the block along different kinds of paths.They calculated that rolling the block required about as much force as moving it along a slippery path. West hasn't tested his idea on larger blocks,but he thinks rolling has clear advantages over sliding.At least,workers wouldn't have needed to carry cattle fat or water to smooth the paths.
Answer: sliding them on smooth paths
Output:
It's widely believed that the stone blocks were moved to the pyramid site by _ .