Answer: Option A
Explanation: The main reason Policy analysts investigate social problems is to find a lasting solution to the problem, or what can be done to prevent such problems from occurring again.
Root Cause is an initiating cause that shows the underlying error to a problem. This definition makes it the best option for the question because it can be deduced that the reason why policy analyst carry out investigation to social problem is to develop a policy solution that attack the problem before it might develop. The best way they can come up with a solution is to determine what the root cause of that social problem is, study it and develop a solution that attacks the problem when ever it develops again.
Proximate cause is the immediate reason behind the problem, is doesn't explain how it was developed. i would say that after root cause, a proximate cause is due to set in, it depends on what type of cause it is and it doesn't provide the evidence or clues of how to develop a solution that can solve the problem. That is why it is not the best answer to the blank space left in the question above.