参考答案

正确答案：A
解析：本题属主旨题，问“短文的主要内容是什么”。第二段中作者提到“…it looks pretty certain thatthe last few decades have been hotter than any comparable period in the last 400 years．”，即过去十几年达到了近四百年的最高温度。第三段中也说到Their conclusion was that a thousand years was reasonable，but not overwhelmingly supported by the data.But the past 400 was so resoundinglythat it fully supports the claim that today’s temperatures are unnaturally warm，…”，即数据不能充分说明地球的气温在过去一千年内一直上升，但能证明过去四百年中地球温度不合自然规律地在变暖。因此，短文的主题为A“地球变暖的趋势”正确。