Here is how i looked at the problem!
The fight is clearly between option B and D.
Stimulus :
construction of many shopping malls who have increased economic activity.
Still the increase in the local economy is much smaller than expected due to construction of shopping malls.
look at option B:It says most of the money spent in the malls is by tourist.
But this statement doesn't remove the discrepancy the question. i.e. it is not important who spends money. the important thing is money is spent in shopping malls and still there is enough increase in local economy!
So ,Imo, the option B in fact increases the proposed Discrepancy!! and so Out!
Look at option D: It says , most of the money would have been spent somewhere in the same community if shopping malls had not been built!
So, this gives us clue that , money spent somewhere in the same community would have increased economic activity in the economy not just in shopping malls.
So, option D definitely solves the discrepancy in the stimulus i.e. Although there is increase in the economic activity in the shopping malls , there is much smaller increase in economic activity in the same community!
Hope this Helps!!!
Phewww...