自由变元代入规则是指对某_______出现的个体变元可用个体常元或用与原子公式中所有个体变元不同的个体变元去代入,且处处代入。
No more having to buy expensive textbooks which you will only use for a year or two and then sell or _______ away.
You can _____ some bottles of wine, or some chocolates, or a bunch of flowers.
A campus emergency ______ occur at any time of the day or night, weekend, or holiday, with little or no warning.
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