第30题: [单项选择]It has been estimated that the earth's surface temperature has increased ______ one quarter to three fourths of a degree since 1850. A. by B. at C. to D. with 参考答案:A 答案解析:[注释] 应该掌握选项中四个介词的不同用法,修饰数字的介词一般为by,所以A项答案正确。全句意思为“据估计,从1850年以来,地表温度增加了0.25--0.75°F”。