Which of the following is NOT a reason solving public problems can be difficult? A. People usually don't have an interest in solving public...

Based on the other choices that are there, yes, I believe that you have it correct.  Choice "A" is not a reason that solving public problems can be difficult.

Although I do think that choice "A" is true for a lot of people.  Assuming that all people have an altruistic spirit that makes them naturally vested in solving public problems is a bad assumption.  There is always going to be a group of people that might recognize the presence of a public problem, but they still have zero desire to solve that problem.  They might not see any personal benefit in solving that problem.  "It doesn't affect me, therefore, why should I care?"  If enough people had that attitude, that would most definitely make solving public problems difficult.  

But like I said before, considering all of the other choices that are there, choice "A" is the best answer to the question.