参考答案：D

解析：[听力原文]26-30 The Global Positioning System (GPS) has become indispensable for soldiers, pilots, hikers, yachtsmen, even bankers, ever since the U.S. Department of Defense started filling the sky with satellites about 25 years ago, in order to improve navigation for fighters, bombers and warships. More recently, GPS has allowed the development of precision-guided weapons, the smart bombs that home in on targets: between Serbia four years ago and this year’s Iraq war, the proportion of such bombs used rose from no more than 3 percent to at least 60 percent. However, the GPS is also an essential prop to countless civil applications; for every military user, there are now 100 civilian users. It provides not only satellite-navigator systems in cars and boats; it is used by Internet service providers, by banks and by surveyors. One day it might be used by air traffic control systems to permit "free flight", in which pilots of commercial aircraft find their own route and stay clear of other aircraft, without the cumbersome business of radio telephone contact with controllers on the ground.

[分析]： 主旨题。 本题要求把握全文结构脉络。本文主要内容是关于GPS(全球定位系统)的应用。其中，前一部分讨论了GPS在军事方面的应用；中间通过However实现转折，后一部分集中讨论GPS的民用。因此能够反映这种脉络，包含全文主要思想的选项d是正确答案。[解题关键] 掌握反映全文结构脉络的信号词，有助于判断全文主旨。本文中第二段首however的使用就反映文章的结构走向。