Responsible for charting the flight paths for sixteen separate airlines--- The phrase modifies flight controllers. So flight controllers should be the followed noun.
So c and are the possible answer but in c "displaying multiple variations of each course" modifier is not clearly modifying the entity.
Hence D is the correct answer.
So c and are the possible answer but in c "displaying multiple variations of each course" modifier is not clearly modifying the entity.
Hence D is the correct answer.
