The correct option is E year only if non-OPEC nations, including Norway, Mexico, and Russia, trim output
In option A, the subjunctive phrase 'were to trim' is used and a subjunctive phrase is used only when we are talking about a hypothetical case. However, in the given context there is nothing hypothetical- the sentence is talking about real economic facts. So, option A is incorrect. Option B '...the output...is trimmed' is in passive form and does not fit the context. In option C, '...the output...would be trimmed' is passive subjunctive and again does not fit the context. The use of 'were trimming' in option D is past progressive which denotes an action that was in progress in the past does not fit with the given context. So, option E is the correct answer.