___是对数据库系统的静态特性的描述,___是对数据库系统的动态特性的描述。
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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