Answer:
D: All of the above.
Step-by-step explanation:
A. All simple machines are useful in some way, weather that be making it easier to lift heavy objects, activating other machines, or something else.
B. Any simple machine must be, well, simple. i. e. have few moving parts.
Take the lever, for example. It has only one moving part, yet it is still very useful.
C. They can be used to do work. Simple machines can be put together to make something that can do work.
Imagine a windmill that generates power, which then is taken by a motor attached to an Archimedes screw. All of these machines are simple, yet they are still used to do work.
