If $f$ is differentiable function, the value of $\underset{h\to 0}{\lim }\frac{{\left[f\left(x+h\right)\right]}^2-{\left[f\left(x\right)\right]}^2}{2h}$  is equal to 

• A

  $f\left(x\right)f\left(x\right)$

• B

  ${\left[f\left(x\right)\right]}^2$

• C

  $\frac{1}{2}{\left[f\left(x\right)\right]}^2$

• D

  $\frac{{\left[f\text{'}\left(x\right)\right]}^2-{\left[f\left(x\right)\right]}^2}{2}$