The function $f(x)=\{[1$ for $x-1],[x$ for $x>-1]\}$ does not satisfy the conclusions of the Mean Volue Thesrem on the closed interval $-1,1$ because

A$)f(-1)=f(1)$

B$)f(-1)$ does not exist

C$)$ function $f$ is not differential on $(-1,1$