The correct option is C x2+2x+1
|x| is not differentiable at x=0
( because at x=0, there is sharp corner.)
[x] is not continuous for all x∈Z
Hence, it will not differentiable for all x∈R
x2+2x+1 is continuous as well as differentiable for all x∈R
sgn x is not continuous at x=0
Hence, it is not differentiable for all x∈R