The Thermal Efficiency of a Heat Engine Is Given by $e = \frac { W _ { a g } } { \left| Q _ { h } \right| }$

The thermal efficiency of a heat engine is given by

A) $e = \frac { W _ { a g } } { \left| Q _ { h } \right| }$ .
B) $e = \frac { \left| Q _ { h } \right| - \left| Q _ { c } \right| } { \left| Q _ { h } \right| }$ .
C) $e = 1 - \frac { T _ { h } } { T _ { c } }$ .
D) all of the formulas above.
E) only (a) or (b) above.