Which is a necessary part input for all heat engines?

A) Steam to act as a working substance

B) An energy source, such as fuel or electrticity

C) A device to generate electrticity

D) Luiqid water to act as a working substance

I believe the answer is B. An energy source such as fuel or electricity.

For example an energy source such as fuel or electricity. For example a heat source generates thermal energy that brings the working substance to the high temperature state. the working substance generates work in the working body of the engine while transferring heat to the colder sink until it reaches a low state of temperature.