问题
选择题
You should not go rafting __________ you know how to swim, and you should always wear
a life jacket. [ ]
A. though
B. unless
C. until
D. if
答案
答案：B
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You should not go rafting __________ you know how to swim, and you should always wear
a life jacket. [ ]
A. though
B. unless
C. until
D. if
答案：B