Which one of the systems described by the following I/P - O/P relation

1.	Which one of the systems described by the following I/P - O/P relations is time invariant
A.	y(n) = n x(n)
B.	y(n) = x(n) - x(n - 1)
C.	y(n) = x(- n)
D.	y(n) = x(n) cos 2pf0n
Answer» C. y(n) = x(- n)

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