问题
选择题
Most whales must come up for air after several minutes, ______ a few can stay under water for an hour or more. [ ]
A. while
B. or
C. for
D. so
答案
答案：A
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Most whales must come up for air after several minutes, ______ a few can stay under water for an hour or more. [ ]
A. while
B. or
C. for
D. so
答案：A