在自然数集N上,下面哪种运算是可结合的?( )。
A、a*b=a-b
B、a*b=max{a,b}
C、a*b=a+2b
D、a*b=|a-b|
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放置元器件的说法中,正确的是()。
A、元件最好对齐到较大的网格上,以利美观
B、贴片元件所在位置的反面可以放置另一个贴片元件
C、穿孔元件所在位置的反面可以放置另一个贴片元件
D、无论什么元件,在PCB上放置越紧密越好
Which of the following system utilities would be used to change a drive type from dynamic tobasic?()
A、System Partition Manager
B、NTBACKUP
C、Device Manager
D、Disk Management
通过哪些方式,不能为封装库添加已有的封装()。
A、从PCB文档中将封装复制粘贴到库中
B、从另一个PCB封装库中将封装复制粘贴到库中
C、从原理图文档中通过复制原理图符号将其链接的PCB封装粘贴到库中
D、在库内复制粘贴
判断下列命题的真假,并说明理由。 (1)如果(A∨C)⇔(B∨C),则A⇔B; (2)如果(A∧C)⇔(B∧C),则A⇔B; (3)如果﹁A⇔﹁B,则A⇔B。
Given that the current directory is empty, and that the user has read and write privileges to the currentdirectory, and the following: Which statement is true?()
A、 Compilation fails.
B、 Nothing is added to the file system.
C、 Only a new file is created on the file system.
D、 Only a new directory is created on the file system.
E、 Both a new file and a new directory are created on the file system.