og13 sc40 求问关于only if的用法

nevercry

"40. The Organization of Petroleum Exporting Countries (OPEC) had long been expected to announce a reduction in output to bolster sagging oil prices, but officials of the organization just recently announced that the group will pare daily production by 1.5 million barrels by the beginning of next year, but only if non-OPEC nations, including Norway, Mexico, and Russia, were to trim output by a total of 500,000 barrels a day.
(A) year, but only if non-OPEC nations, including Norway, Mexico, and Russia, were to trim output
(B) year, but only if the output of non-OPEC nations, which includes Norway, Mexico, and Russia, is trimmed
(C) year only if the output of non-OPEC nations, including Norway, Mexico, and Russia, would be trimmed
(D) year only if non-OPEC nations, which includes Norway, Mexico, and Russia, were trimming output
(E) year only if non-OPEC nations, including Norway, Mexico, and Russia, trim output

我想问的是关于A选项，为什么不对。but only if感觉读起来很顺，而且看CD帖子里有一个句子：I will tell you the secret, but only if you promise not to tell others.不知道这个句子对不对。
另外，only if可以看做是虚拟语气吗？

求大神解答！多谢！

shua2015

都不对。but前面有逗号做连词后面要加完整的句子，否则是 run-om.  去掉逗号我也不知道了

alzn2765

这就是个简单的条件状语从句，主句用将来时，条件句用一般现在时。初中学的那个。
用不着虚拟语气，如果用了虚拟语气就是表达那几个国家减产是天方夜谭一样的事情的意思。赤裸裸的挖苦啊！咱不能把人家都当成谢耳朵

AMBER513

看一下！