I believe the answer should be A.
When we say that this year the two parties are working together, we could use either of the following verbs:
• they are collaborating (an ongoing process)
• they will collaborate (a future event)
• they collaborated (a past event that has ended)
However, they collaborate (a simple present statement) is incorrect. Which eliminates options B, D, and E.
Both the remaining options A and C, use the correct form of verb with the rising inequality level (has increased)
However, C begins by stating "Populists and Professors are rarely seen eye to eye" which means it is us (external spectators - the third person) who don't see them the same.
While A begins by stating "Populists and Professors rarely see eye to eye" which is more appropriate as it means that it is the two parties who see each other as holding contrasting views.
Posted from my mobile device