18. An acre of average ffarmland produces only about 400 pounds of grain amaranth, as against 2,400 pounds per acre, or six times as much, for wheat. It follows that whenever the grain-amaranth price is projected to be more than six times the projected price of wheat, farmers wishing to maximize profits will grow grain amaranth rather thant wheat. The argument above is based on which of the following assumptions? (A) An acre's worth of grain amaranth is no more expensive to grow and bring to market than an acre's worth of wheat. (B) There is no crop that produces a higher yield in terms of pounds harvested per acre than wheat. (C) By choosing which crops to grow, farmers can exert a significant influence on the prices of those crops. (D) Farmers are no less motivated by th desire to mazximize profits than are other occupational groups. (E) Prices of grain crops can change faster than farmers can change the acreage devoted to various grain crops. 推理：“若amaranth的价格比小麦高出6倍，则种植amaranth”。价格是主要或者唯一的因素。 A是否是争取的选项呢？ | 
