问题
选择题
Many possible means ___been tried, but ___worked. [ ]
A. have, none
B. has, a few
C. has , none
D. have , a few
答案
答案：A
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Many possible means ___been tried, but ___worked. [ ]
A. have, none
B. has, a few
C. has , none
D. have , a few
答案：A