ANSWER
C)
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Step-by-step explanation
A linear function is a function whose graph is a straight line.
The graph of y=x is a straight line.
The graph of y=3x -7 is also a straight line.
The graph of y=x² is a parabola.
This graph is not a straight line .
It is a non-linear function.
y=3 and y=13 are also straight lines.
The correct choice is C.