问题
选择题
We won't be able to learn English well _____ we learn enough words by heart and do enough reading. [ ]
A. as
B. once
C. when
D. unless
答案
答案：D
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We won't be able to learn English well _____ we learn enough words by heart and do enough reading. [ ]
A. as
B. once
C. when
D. unless
答案：D