Friction is considered as a necessary evil. The friction helps in many ways in our day to day life. We hold things, walk on the surface etc. are supported by friction. But it causes loss of efficiency of any machine.
In machine, there will be friction between various parts of it. Friction opposes the relative motion between them.Due to this friction, much more amount of heat will be produced which reduces the efficiency of the machine i.e the desired output is not obtained.
Hence the correct answer to the question will be friction i.e thermal energy is lost in all machines due to the force of friction