In the text below some words are missing. Drag words from the box below to the appropriate place in the text. To undo an answer choice, drag the word back to the box below the text.
下面的文本缺了一些词。请把词框里的词拖到文中合适的位置；要撤销选择，把词拖回文本下方的词框即可。
the past two decades, around a third of the world's mangrove swamps have been for human use, with many turned into valuable shrimp farms. In 2007 an economic study of such shrimp farms in Thailand showed that the commercial profits per hectare were $9,632. If that were the only , conversion would seem an excellent idea. However, proper shows that for each hectare government subsidies formed $8,412 of this figure and there were costs, too: $1,000 for pollution and $12,392 for losses to ecosystem services. These comprised damage to the supply of foods and medicines that people had taken from the forest, the loss of habitats for fish, and less buffering against storms. And because a given shrimp farm only stays for three or four years, there was the additional cost of restoring them afterwards.
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