问题
选择题
I'm sorry, but I'm too busy to help you now. I can only do one thing .[ ]
A. at one time
B. at a time
C. at time
D. at the time
答案
答案：B
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I'm sorry, but I'm too busy to help you now. I can only do one thing .[ ]
A. at one time
B. at a time
C. at time
D. at the time
答案：B