Chapter 3 - Polynomial and Rational Functions - 3.6 Variation - 3.6 Exercises - Page 388: 17

C.

As we know, a linear function can always be displayed as: $y=mx+b$ In this case, the equation $y=kx$ is easily recognized as a linear function, with $k$ replacing $m$ and $b=0$. Thus, the graph describing this equation should be linear. Only C satisfies this requirement.