If you’ve gone to the same seashore for several years, you may have noticed that the beach gets smaller every year. The wind and

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问题     If you’ve gone to the same seashore for several years, you may have noticed that the beach gets smaller every year. The wind and the waves carry the beach out to sea, bit by bit. Most shore towns try to fight the beach changes caused by ocean currents and the tides. Some dig sand out of backwater bays and dump it on the beachfront. Others build wooden piers and jetties made to keep currents away from the beach.
    A type of artificial sand that has been developed might be able to slow down beach erosion. Strangely, this new kind of sand is made of ground glass! You might think that walking barefoot on ground glass would be painful. But it’s not. The reason is very simple. Sand and glass are made of the same kind of material, called silicate. When glass is ground very finely, you get a sand-like substance that is harder than real sand. The size of the pieces can be controlled. Larger pieces won’t be as easily affected by the wind and waves. So, a beach covered with artificial sand would last longer than a beach with real sand.
    A wonderful thing about artificial sand is that it can be made from waste glass. But making artificial sand costs three times as much as using conventional methods of beach protection. So, it is not likely that sand made of glass will be used in the near future.
The subject of this passage is ______.

选项 A、summer vacations
B、the seashore
C、artificial sand
D、sand and water

答案C

解析 这篇短文讲的是为了保证沙滩的面积不再缩小,人类使用人造沙。选项C是正确的。
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