Find the Torsion of the Space Curve $\tau = - \frac { \tanh ^ { 2 } t } { 2 }$

Multiple Choice

Find the torsion of the space curve.
-r(t) = (cosh t) i + tj + (sinh t) k

A) $\tau = - \frac { \tanh ^ { 2 } t } { 2 }$
B) $\tau = - \frac { \operatorname { sech } ^ { 2 } t } { 2 }$
C) $\tau = \frac { \tanh ^ { 2 } t } { 2 }$
D) $\tau = 0$