Okay first of all 'flux' means the action or process of flowing or flowing out. or continuous change. Now ' influx' means , an arrival or entry of large numbers of people or things or an inflow of water into a river, lake, or the sea. So know that you know that the answer to this question would be, A or D to figure out which one is the best answer we need to read the sentence again.' There was an outflux of tenants from our apartment building. That should be a good clue to the owners that they need to make changes. It is time they do something about the heating and plumbing problems.' So the best sutible answer would be, A.The tenants are moving out of the apartment building.