Almost all time, if a argument talks about profit, then definitely argument is talking about input cost and earnings.
Here we are told that bus fare is greater in morning than that in evening. We understand by "bus fare" is total fare collected.
Now assumption to establish the conclusion " higher profit in morning than in evening" should talk about cost side.
Now only option B clearly states that fuel cost is not higher in morning than in evening.
Option A talks about volume of passengers which is already considered while calculating bus fare in given argument.
Option C talks about fare comparison between private and public transport company which is not argument concern.
Option D says different routes lead difference in fare. But difference could be positive and negative.
Option E is clearly out as we are not worried whether passengers are mindless or prudent.