A. must contain unique values. B. cannot be CAST to other data types. C. is created using the CREATE DISTINCT command. D. contains a value that was automatically calculated from values in other columns.
A. 印刷媒介 B. 电子媒介 C. 平面媒介 D. 单向媒介 E. 互动媒介
A. 1千瓦小时 B. 1千瓦秒 C. 1欧姆小时 D. 1伏特小时
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