以企业为中心确定经营方向才能满足顾客需要。
You（）buy some reference books when you go to college. ["could","will have to","must to","might"]
计算单位产品或服务的成本价格：算出一个月的总成本，再除以当月的产品数量，就能得出你的产品或服务的单价。
同时具备人口、购买力以及购买欲望三个条件才能构成市场。
The atmosphere（）certain gases mixed together in definite proportions. ["composes of","is made up","consists of","makesup of"]
什么是系统？什么是封闭系统和开放系统？
