问题
选择题
With some technical problems to be solved, it may be a while _____ the system is put into use. [ ]
A. when
B. after
C. since
D. before
答案
答案：D
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With some technical problems to be solved, it may be a while _____ the system is put into use. [ ]
A. when
B. after
C. since
D. before
答案：D