本题考查近义词辨析。选项A意为 “ 有限的” ，选项B意为 “ 隐藏的” ，选项C意为 “ 短的，缺乏的” ，选项D意为 “ 贫困的” 。替换词意为“ 不足”。该题主句为主 系表结构，复杂的名词短语（the biggest challenge for hikers in this part of the mountain range ) 作主语，is是系动词， that引导的从句（water is scarce)作表语。根据语言习 惯，选项A恰当。选项C虽然也可以，但相比较A , limited更常用。
[参考译文]在这片山脉中，徒步旅行者面临的最大挑战是缺水。
[词汇拓展] scarce, short, limit语义相近，下面是词典对这三个词的英文释义：
scarce: If something is scarce,there is not enough of it.
short： If you are short of something or if it is short, you do not have enough of it.
limit： Something that is limited is not very great in amount, range, or degree.