单选题 How much of the world's land surface is at risk of becoming desert?

A、 Less than ten million square kilometers.
B、 Twenty million square kilometers.
C、 Mom than twenty million square kilometers.
D、 30% of the world's land surfac

【正确答案】 C

【答案解析】文章第二段中间有一句话“Twenty million square kilometers，an area twice the size of Canada，is at a high to very high risk of becoming desert．With a further 1.25 million square kilometers under moderate risk．”，这句话是说，2000万平方公里的土地面临着成为沙漠的高危险，而125万平方公里的土地有中度危险，加起来就是答案C——超过2000万平方公里的土地面临着成为沙漠的危险。