Critical Reasoning

Gortland has long been narrowly self-sufficient in both grain and meat. However, as per capita income in Gortland has risen toward the world average, per capita consumption of meat has also risen toward the world average, and it takes several pounds of grain to produce one pound of meat. Therefore, since per capita income continues to rise, whereas domestic grain production will not increase, Gortland will soon have to import either grain or meat or both.
Which of the following is an assumption on which the argument depends?

(A) The total acreage devoted to grain production in Gortland will not decrease substantially.
(B) The population of Gortland has remained relatively constant during the country's years of growing prosperity.
(C) The per capita consumption of meat in Gortland is roughly the same across all income levels.
(D) In Gortland, neither meat nor grain is subject to government price controls.
(E) People in Gortland who increase their consumption of meat will not radically decrease their consumption of grain.


Please take a look my problem and see what is wrong with my reasoning.

I understand that we need an assumption that indicates the grain consumption, that is not used to produce meat, does not decrease more than that, used to produce meat, increases.

Since the correct choice is an assumption, it must be necessary. However, I cannot explain why we need to know about the consumption of people who increase their meat consumption.
What makes those people so special that we need to know about their grain consumption?
How about people who do not increase their meat consumption? If their grain consumption decreases substantially then the choice E may not necessary to make the conclusion true.

Even I negate the choice, it does not break the conclusion at all because the choice overlook the grain consumption of people who do not increase meat consumption.

Thank you.