GWD-7-Q26 有关v-ing修饰对象的问题 求解答~

（66）    GWD-7-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.
   
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

有两个点不太明白
一、正确答案是E选项， 我想问的是including在这里是做的定语修饰nation吗 我觉得如果是作定语的话 including前的逗号应该去掉

，v-ing形式不是只有两种情况1、做s的定语 2、做svo的结果状语

二、还有一个一直有疑问的问题
有没有这种句型
SVO，if SVO，v-ing此时的-ing是修饰紧挨着他的if从句的SVO，还是修饰主句SVO