参考范文：
The main factors responsible for the decreased productivity of agricultural land in North America, Europe, and Oceania during the 1990s were summarized in a pie chart and a table.
the most serious problem was over-grazing. It has caused the world to lose 35% of agriculture land. This problem is followed closely by deforestation and over-cultivation.
The area that has lost most proportion of its agriculture land was Europe at 23% However, Oceania and North America was not as badly affected, losing 13% and 5% of its farmland respectively.
Surprisingly, the main problem faced by each area is different from one another. The problem with over-grazing is especially serious in Oceania, resulting in 11.3% of its land unsuitable for agriculture. On the other hand, deforestation that caused 9.8% of agriculture land unusable was the major problem faced by the European farmers. Although over-cultivation was the primary threat in North America, it was not a problem at all in Oceania.
In conclusion, over-grazing was the main cause of worldwide degradation in 1990s. Europe’s percentage of degradation was largest of all three regions and all three regions had different predominant causes.
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