Final answer:
The statement about power transmission devices is true; they are key components that transmit energy in a mechanical system for work, but the efficiency of simple machines is always below 100% due to energy losses such as heat from friction.
Step-by-step explanation:
The statement that power transmission devices are all components of the mechanical system which transmit energy to the part of the machine performing the work is true. This is because power transmission involves energy transfer within mechanical systems where certain deviceIdes, such as gears, belts, and shafts, play a key role in moving energy from the source to where it is needed for work. Within this context, the efficiency of a simple machine is always less than 100 percent due to some amount of input work being lost as heat energy because of friction.