With regard to the physics of power systems used operate robots, which statement or statements is most correct?

chemical batteries produce AC power

hydraulics involves the compression of liquids

hydraulics involves the compression of air

pneumatics involve the compression of air

With regard to the physics of power systems used operate robots, which

1.	With regard to the physics of power systems used operate robots, which statement or statements is most correct?
A.	hydraulics involves the compression of liquids
B.	hydraulics involves the compression of air
C.	pneumatics involve the compression of air
D.	chemical batteries produce AC power
Answer» D. chemical batteries produce AC power