If $\mathrm{f}\text{'}\left(\mathrm{x}\right)=\left|\begin{array}{ccc}\mathrm{mx}& \mathrm{mx}-\mathrm{p}& \mathrm{mx}+\mathrm{p}\\ \mathrm{n}& \mathrm{n}+\mathrm{p}& \mathrm{n}-\mathrm{p}\\ \mathrm{mx}+2\mathrm{n}& \mathrm{mx}+2\mathrm{n}+\mathrm{p}& \mathrm{mx}+2\mathrm{n}-\mathrm{p}\end{array}\right|$, then y = f(x) represents 

• A

  a straight line parallel to x-axis

• B

  a straight line parallel to y-axis 

• C

  parabola

• D

  a straight line with negative slope