问题补充：
Every means, but none proved.
A. have tried; a success
B. have been tried; successful
C. has tried; to be successful
D. has been tried; successful
答案：
A. have tried; a success
B. have been tried; successful
C. has tried; to be successful
(答案→)D. has been tried; successful
解析：考查主谓一致：means是单复数同形的名词，单复数取决于修饰词，这句话means用every修饰，说明是单数，谓语用单数，而且means和try是被动关系，用has been tried，第二空的prove是连系动词，后面接形容词做表语。句意：每种办法都被尝试过了，但没有一个证明是成功的。选D。
