Answer: E - year only if non-OPEC nations, including Norway, Mexico, and Russia, trim output
Explanation: From the above question, we are looking for the best constructed sentence among the options given.
Looking through all the options, A and B with the phrase ...'but only if' is wrong.
Options C and D has some grammatical issues at the end of each statement which made them both not correct.
The only option we are left with is the option E which states that 'year only if non-OPEC nations, including Norway, Mexico, and Russia, trim output' is correct.