The steady flow energy equation can be applied to which of the above systems?

Question

Consider the following system.  

         1.   An electric heater

         2.   A gas turbine

         3.   A reciprocating compressor

         The steady flow energy equation can be applied to which of the above systems?           

(a) 1 and 2 only    (b)1 and 3 only

(c) 1, 2 and 3       (d) 2 and 3 only