小题1:D
小题2:B
小题3:A
小题4:C
试题解析：本文介绍了又胖又害羞而被大家取笑的桑德斯从十五岁生日收到山地自行车开始改变到成为了跨越南海岸的南极和南极洲的第一人的非凡成就。
小题1:细节理解题。根据第二段It was a mountain bike he received for his 15 th birthday that changed him. At first he went biking alone in a nearby forest. Then he began to ride the bike along with a runner friend. Gradually, Saunders set up his mind on building up his body, increasing his speed and strength.可以判断出Ｄ正确。
小题2:细节理解题。根据第三段划线部分后Greatly interested, Saunders read all he could about North Pole explorers and adventures, then decided that this would be his future. 可以判断出Ｂ正确。
小题3:细节理解题。根据第二段At first he went biking alone in a nearby forest.可以判断出ｃ，根据第二段最后At the age of 18, he ran his first marathon.可以判断出ａ，根据第五段开头Saunders has since become the youngest person to ski alone to the North Pole可以判断出b,根据最后一段Next October, Saunders, 27, heads south from the coast of Antarctica to the South Pole and back可以判断d,由以上内容可以判断C正确。
小题4:总结归纳题。本文从第一段开始介绍Saunders，胖还很害羞被大家所取笑，到最后他成为了跨越南海岸的南极和南极洲的第一人，所以Ｃ正确。