The context refers to an ideal situation with a condition.
Thus, it means 'we think salaries ought to go up'. Here, the phrasal verb 'go up' indicate becoming higher or more than what something previously was. The phrasal modal 'ought to' means an expectation that something happens that should already have happened. Thus, option D concurs with the context.
Option A is incorrect as it implies that salaries have already increased.
Option B is incorrect as it indicates a time when salaries did increase.
Option C is incorrect as it indicates that this time salaries did increase and this was the right time.
Thus, option D is correct.