◎ 题干
My sister isn't in. _______ she comes back, I'll let her call you back.  
[     ]
A. While
B. Until
C. Before
D. When
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◎ 解析
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◎ 知识点
    根据n多题专家分析,试题“My sister isn't in. _______ she comes back, I'll let her call you back. [ ]A. While B. Until C. Before D. When …”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。