Let f′(x)=∣x−1∣ for all real x, and suppose f is twice differentiable wherever possible. Which of the following statements about f′′ is correct?
a) f′′(x)=0 for x=1, and f′′(1) does not exist
b) f′′(x) does not exist for any real x
c) f′′(x)=−1 for x<1, f′′(x)=1 for x>1, and f′′(1) does not exist
d) f′′(x)=1 for x<1, f′′(x)=−1 for x>1, and f′′(1) does not exist