【单选题】【消耗次数：1】
精馏中引入回流，下降的液相与上升的汽相发生传质使上升的汽相易挥发组分浓度提高，最恰当的说法是（ ）。
①
液相中易挥发组分进入汽相和汽相中难挥发组分进入液相必定同时发生
②
液相中易挥发组分进入汽相
③
汽相中难挥发组分进入液相
④
液相中易挥发组分和难挥发组分同时进入汽相，但其中易挥发组分较多????????
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