[逻辑小分队] 【求助】13OG书，P37，我问题都木有看懂。。。

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?什么意思啊？？

　　(A) The total acreage devoted to grain production in Gortland will soon decrease.

　　(B) Importing either grain or meat will not result in a significantly higher percentage of Gortlanders' incomes being spent on food than is currently the case.

　　(C) The per capita consumption of meat in Gortland is increasing at roughly the same rate across all income levels.

　　(D) The per capita income of meat producers in Gortland is rising faster than the per capita income of grain producers.

　　(E) People in Gortland who increase their consumption of meat will not radically decrease their consumption of grain.