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注意：1. 每处错误及其修改均仅限一词;
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Welcome to the Great Wall. Measured more than 6,000 kilometers in length, the Great Wall is known as the long wall in the world. It had a long history of more than 2,000 years. That is amazing about the Great Wall is that it is main made of stones and bricks, and that all the construction was done by hand. As it was used to protecting the country from foreign invaders, every a few hundred meters along the Great Wall, there was a watchtower. Now, as a symbol of China, the Great Wall has become one of the most famous tourist attraction in the world. There is no wonder that the Great Wall attracts thousands foreign tourists every year.
2 . If you live in a town or city on the edge of a desert or coastline where sand dunes form, you might understand the threat they can have. It’s, sometimes, a piece of cake for them to cover roads, buildings, farms and other man-made developments with their unpredictable movements. Thus, figuring out how they move is important for preventing some natural disasters.
Now scientists have discovered that dunes have been secretly moving in ways we never knew before. There are different explanations on dune interaction, however, Karol Bacik, first author on the new dune study, and his colleagues have found a new one for dune movement. The researchers employed high-speed cameras to observe how dunes separated by distance can act as if they’re connected.
It turns out, currents flowing over sand dunes can carry “information” to other dunes downstream in the form of swirls(旋涡). For instance, as wind or water flows over the top of a dune, it slightly moves. This can generate “swirls” on the back of a downstream dune and push it in a direction opposite the movement of the front dune.
It’s the first time that researchers were able to provide causal explanations for some of these strange, previously unpredictable movements. The team also hopes to get out of the laboratory and into the real world, to see if their models can be applied to dune movements in complex natural systems. They plan to use satellite images over large deserts to track groups of dunes over long periods.
Perhaps they can start to alter the dune marching orders in the near future. Imagine being able to tell a dune field exactly how you want it to move. That’s the idea that this research might one day make possible.
1. We can learn that the purpose of the study is to _________.| A．stop the sand dunes from moving around |
| B．figure out the track of sand dune movements |
| C．prove the interaction of dunes with each other |
| D．examine a model of sand dunes in the real world |
| A．A study. | B．An interaction. | C．An explanation. | D．A dune. |
| A．A sand dune communicates with another only by currents. |
| B．Swirls on the back of a dune are the power to move itself. |
| C．Some strange dune movements have got causally explained before. |
| D．Researchers think it unnecessary to study further on the dune models. |
