Let $f ( z ) = \frac { e ^ { z } - 1 } { z ( z - 1 ) }$ be defined on the extended complex plane $\mathbb { C } \cup \{ \infty \}$. Which of the following is/are true?\\
(A) $z = 0 , z = 1 , z = \infty$ are poles.\\
(B) $z = 1$ is a simple pole.\\
(C) $z = 0$ is a removable singularity.\\
(D) $z = \infty$ is an essential singularity.