Linux
The command chmod 761 letter is equivalent to

chmod u = rwx, g = rw, o = x letter
None of the listed here
chmod 4=7, g = 6, o = 1 letter
chmod a = 761 letter

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Linux
The physical layer of a network

controls error detection and correction
None of these
constructs packets of data and sends them across the network
All of these
defines the electrical characteristics of signals passed between the computer and communication devices

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