Let $f\left(x\right)=10-\left|x-5\right|,x\in R$, then the set of all values of $x$ at which $f\left(f\left(x\right)\right)$ is not differentiable is

• Correct answer
  A

  $\left\{\mathrm{0,5},10\right\}$
• B

  $\left\{\mathrm{5,10}\right\}$
• C

  $\left\{\mathrm{0,5},\mathrm{10,15}\right\}$
• D

  $\left\{\mathrm{5,10,15}\right\}$

Hence, the correct answer is option: 'A'.