题目选项分析

Edgarton has long been narrowly self-sufficient in both coal and steel. However, as more and more people have moved to Edgarton, more coal needs to be burned to heat their homes. Because coal is an important component of steel, if the influx of new residents continues, Edgarton will soon have to import either coal or steel.

Which of the following is an assumption on which the argument depends?

【选项】Operational costs for coal producers are higher than the operational costs for steel producers.