计算机三级2022考试试题试卷(7V)

1. [单选题]Every value in arelation must be().

A. composite(复合的)and single-valued
B. single-valued
C. notnull and single-valued
D. simple and single-valued

2. [单选题]POP3.服务运行的默认端口号为( )

A. 25
B. 40
C. 21
D. 110

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