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  3. A new study, published in the international scientific journal Nature, revealed that an estimated half a million cubic kilometer

A new study, published in the international scientific journal Nature, revealed that an estimated half a million cubic kilometer

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问题     A new study, published in the international scientific journal Nature, revealed that an estimated half a million cubic kilometers of low-salinity water are buried beneath the seabed on continental shelves around the world.
    "The volume of this water resource is a hundred times greater than the amount we’ve extracted from the Earth’s sub-surface in the past century since 1900," says lead author Dr. Vincent Post of the National Centre for Groundwater Research and Training (NCGRT) and the School of the Environment at Flinders University.
    Dr. Post said that while scientists knew of freshwater under the seafloor, they thought it only occurred under rare and specific conditions.
    These reserves were formed over the past hundreds of thousands of years when on average the sea level was much lower than it is today, and when the coastline was further out, Dr. Post explains.
    "So when it rained, the water would infiltrate into the ground and fill up the water table in areas that are nowadays under the sea.
    "It happened all around the world, and when the sea level rose when ice caps started melting some 20,000 years ago, these areas were covered by the ocean.
    "These aquifers (含水层) protected from seawater by layers of clay and sediment that sit on top of them."
    The aquifers are similar to the ones below land, which much of the world relies on for drinking water, and their salinity is low enough for them to be turned into potable water, Dr. Post says.
    "There are two ways to access this water—build a platform out at sea and drill into the seabed, or drill from the mainland or islands close to the aquifers.
    "Freshwater on our planet is increasingly under stress and strain so the discovery of significant new stores off the coast is very exciting. It means that more options can be considered to help reduce the impact of droughts and continental water shortages."
    But while nations may now have new reserves of freshwater offshore, Dr. Post says they will need to take care in how they manage the seabed: "For example, where low-salinity groundwater below the sea is likely to exist, we should take care not to contaminate it.
    Dr. Post also warns that these water reserves are non-renewable: "We should u; them carefully—once gone, they won’t be refilled until the sea level drops again."
Why are many aquifers free from being destroyed by seawater?
选项 A、Because seawater is much saltier than reserves under the sea.
B、Because aquifers have self-healing mechanism.
C、Because aquifers are protected by layers of clay and sediment.
D、Because seawater can refresh aquifers when they are mixed.
答案C
解析 细节题。根据题干中的flee from being destroyed by seawater可定位是原文第七段，该段提到海底泥土和沉积物保护这些海底地下水，以免受海水侵害。故选C。
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