Remember to identify the conclusion whenever you do an CR question. Now use the Negate approach with answer E:

Let's say: Normally Gortland consumes: 1000 Grain and 1000 Meat, equal to what the country can produce; and the exchange rate is 4G --> 1M

If now the consumption is: 800G and 1100M --> Gortland can exchange extra 200G to 50M, so it actually produces 1050M, still need to import another 50M
If now the consumption is: 700G and 1100M --> exchange extra 300G to 75M, so still need to import another 25M
If now the consumption is: 600G and 1100M --> exchange extra 400G to 100M and Tah-da! Gotrland does not have to import anything at all --> against the conclusion

That's why we need to assume the consumption of grain will not decrease radically. The OA is E