Final answer:
Piston-driven ventilators work by using pressurized gas to drive the movement of the piston.
Step-by-step explanation:
Piston-driven ventilators work by using pressurized gas to drive the movement of the piston. This movement creates changes in pressure within the ventilator circuit, causing air to flow into or out of the patient's lungs.
Therefore, the correct answer is A) Pressurized gas drives movement of the piston.
The other options mentioned in the question are not true regarding piston-driven ventilators. They are capable of working in pressure support mode, do not necessarily require wall outlet electricity at all times, and do not require a servo-controlled valve to prevent circuit pressure from exiting to the scavenging system during inspiration.
So, the correct answer is A) Pressurized gas drives movement of the piston.