but only if -----redundancy?

Q26:

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.

1. year, but only if non-OPEC nations, including LACE>NorwayLACE>, LACE>MexicoLACE>, and LACE>RussiaLACE>, were to trim output
   
2. year, but only if the output of non-OPEC nations, which includes LACE>NorwayLACE>, LACE>MexicoLACE>, and Russia, is trimmed
   
3. year only if the output of non-OPEC nations, including Norway, Mexico, and Russia, would be trimmed
   
4. year only if non-OPEC nations, which includes Norway, Mexico, and Russia, were trimming output
   
5. year only if non-OPEC nations, including Norway, Mexico, and Russia, trim output

答案选E，从其它方面可以得出，但是我想问一下

but only if 是不是redundant 的用法呢？