◎ 题干
This is an illness that can result in total blindness _____ left untreated.
[     ]
A. after
B. if
C. since
D. unless
◎ 答案
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◎ 解析
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◎ 知识点
    根据魔方格专家分析,试题“This is an illness that can result in total blindness _____ left untreated. [ ]A. after B. if C. since D. unless …”主要考查了你对  【从属连词】  等知识点的理解和应用能力。关于这些知识点的“档案”,你可以点击相应的链接进行查看和学习。