问题
选择题
My sister isn't in. _______ she comes back, I'll let her call you back. [ ]
A. While
B. Until
C. Before
D. When
答案
答案：D
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My sister isn't in. _______ she comes back, I'll let her call you back. [ ]
A. While
B. Until
C. Before
D. When
答案：D