Let $f(x)=\lfloor x\rfloor$ Which of the Following Is True?

A) $f$

Multiple Choice

Let $f(x) =\lfloor x\rfloor$
Which of the following is true?

A) $f$ is discontinuous at 0.
B) $f$ has a derivative at 0.
C) $f$ has a corner at (0,0) .
D) $f$ has a horizontal tangent line at (0,0) .
E) $f$ has a vertical tangent line at (0,0) .