标题: og13 sc40 求问关于only if的用法 [打印本页] 作者: nevercry 时间: 2015-4-27 21:36 标题: og13 sc40 求问关于only if的用法 "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？