Which of the following statement is correct as regard to the difference between a machine and a structure?

• A. The parts of a machine move relative to one another, whereas the members of a structure do not move relative to one another.
• B. The links of a machine may transmit both power and motion, whereas the members of a structure transmit forces only.
• C. A machine transforms the available energy into some useful work, whereas in a structure no energy is transformed into useful work.
• D. all of the mentioned