alternative P42 第二段第二行，“by variable exp, we mean that they depend on the level of occupancy, whereas fixed exp do not depend on the level of occupancy"
EXAMPLE 20: fixed portion is ($4 * 0.25 * 200,000) / (0.8 * 200,000)=1.25. 其中0.8来自于 the building is 80% occupied。
这里是否有矛盾？为何fixed部分需要除以实际的占用面积，教材里不是说了do not depend on the level of occupancy么，求教。
