题目内容：
20. Living in the desert involves a lot of problems, ____water shortage is the worst.
(A) not to mention
(B) of which
(C) let alone
(D) for what
参考答案：
选择题：20.Living in the desert involves a lot of problems
- 题目分类：郑州工程技术学院-大学英语（2）.
- 题目类型：选择题
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Living in the desert involves a lot of problems, ____water shortage is the worst.
(A) not to mention
(B) of which
(C) let alone
(D) for what