问题补充：
Living in the central American desert has its problems, obtaining water is not the least .
A. of which
B. for what
C. as
D. whose
答案：
(答案→)A. of which
B. for what
C. as
D. whose
解析：句意：居住在美洲沙漠中部有它自身的问题，取水还不是最基本的问题。which引导非限制性定语从句，of which表示它的问题是，故选A
