Below is a text with blanks. Click on each blank, a list of choices will appear. Select the appropriate answer choice for each blank.
下面的文本有一些空格。点击每个空格会出现一组选项，请为每个空格选出最合适的答案。
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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