I have looked at this question a couple of different ways right now and I think that diagramming it would not be the optimal approach. There is the one conditional statement that can be diagrammed, but this is not the main focus of the stimulus, nor would it lead to any real inferences.
I believe that a better approach for this question would be to try to analyze the information presented as it is. Simplifying as you go.
We learn that household indebtedness is regarded by some theorists as causing recession. It was high before the recent recession. But on the other hand, the value of assets owned by households was also high.
Then the passage begins to get into a complicated discussion of if affluent owned most assets and if most debt owed by low income, then high debt levels may have led to the recession. Then they show that this condition doesn't hold up. The passage then concludes that household indebtedness is not the cause.
This is what we find in answer choice A. An alternate phrasing of the conclusion in the passage.
I hope this helps. Please let me know if you have any other questions or would like me to elaborate further.