Let $f ( x ) = \ln ( \operatorname { sech } x )$

Multiple Choice

Let $f ( x ) = \ln ( \operatorname { sech } x )$ Then $f ^ { \prime } ( x )$ is

A) $\operatorname { csch } ^ { 2 } x$
B) $\operatorname { coth } x$
C) $- \operatorname { coth } x$
D) $- \tanh x$
E) $\tanh x$