题目

Jenna, a popular girl from Westwood Middle School, had graduated first in her class and was ready for new 26 in high school.   _27 , high school was different. In the first week, Jenna went to tryouts (选拔赛) for cheerleaders (拉拉队队员). She was competing against very talented girls, and she knew it would be 28 for her to be selected. Two hours later, the 29 read a list of the girls for a second tryout. Her heart 30 as the list ended without her name. Feeling 31 , she walked home carrying her schoolbag full of homework. Arriving home, she started with math. She had al阅读下列材料，完成相关问题。【材料一】西沙群岛地处热带中部。以永兴岛为例，极端高温34．9℃。极端低温15．3℃，年平均气温26．5℃。年降雨量1505毫米。【材料二】甘泉岛位于中国西沙群岛永乐环礁上，是西沙群岛中出露最晚的岛，地势较高，最高处8．3米，中心低平，四周为沙提围烧，再往外围是珊瑚礁环绕的浅滩;东南侧有浅水码头，岛上有一口清末古井，井水清澈甘甜适宜使用，也是西沙为数不多具有淡水的岛屿。【材料三】南海诸岛及甘泉岛图。（1）分析西沙群岛终年高温，夏无酷暑，雨量丰沛的成因。（2）从地质作用角度分析环岛沙堤的形成过程。（3）试分析甘泉岛上井水甘甜的原因。（4）如果定居甘泉岛，简析在基础设施建设时，应侧重考虑哪些因素。