This is a weaken question. The Prime Minister desires to aid the local economy (that's the desired consequence) by providing free rice. The underlying assumption is that, if people can't buy the rice they need, the economy will suffer; if people can buy the rice they need, the economy will be helped. Consider each choice in turn:

(A) This strengthens the argument: The coupons will make people more confident in the economy.
(B) This, if anything, strengthens the argument; the subsidized rice will not cost the government as much as it might otherwise. For the most part, though, it is not relevant to the argument.
(C) Again, this appears to strengthen the argument--it shows how important rice is to citizens. Like (B) though, it isn't directly related to the economy.
(D) This is correct. While the argument emphasizes the importance of the domestic market, this choice shows us that the export market has a direct effect on the health of the domestic economy. If the government acquires a large amount of rice, it is likely that rice exports will be curtailed by that amount, thus harming the economy.
(E)This is irrelevant; the argument would still be valid if only a large percentage of citizens required the coupons.