泾县环球影城票价:英语选择题一道（说出原因）悬赏50追加得分

I think you have misunderstood the meaning of this part of the sentence: "Obtaining water is not the least". Now let's analyze its real meaning:

the least = the one that is the lowest in rank = the least serious /the least important

NOT the least = NOT the one that is the lowest in rank = NOT the least serious = Quite serious

not the least of these problems = a quite serious problem

Of which obtaining water is not the least = obtaining water is not the least of these problems = 获取水 就是其中一个 严重 的问题

That's why you should choose A as the correct answer.

这应该是非限制性定语从句，“obtaining water ”is one of the problems, not the only problem.
所以是of which
我们有这样说的:Which of these pens do you like best? 就是用的 which of

个人认为选C
居住在澳洲中部的沙漠上还有另外的问题，不仅仅是能不能保持住水的问题。
定语从句，用AS来代前面的一句话。

obtaining water是这些problems中的一种，所以应该用表所属关系的of which.
整句话用顺序写出来就是：Living in the central Australian desert has its problems,obtaining water is not the least of these problems.

应该是A,至少我认为选A.这一题考的是非限制性定语从句.which代指前面的its problems.of which即指of its problems.即翻译为"在这些问题之中"

这是定语从句，WHICH是定物的，而且两句间有“，”所以加OF。