问题
选择题
Every possible means ____, but none ____ successful．
A．has tried; has proved
B．tried; proves
C．has been tried; proves
D．is being tried; is proved
答案
答案：C
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Every possible means ____, but none ____ successful．
A．has tried; has proved
B．tried; proves
C．has been tried; proves
D．is being tried; is proved
答案：C