Gasses come from the anesthesia machine and exit the common gas outlet flow through a circular breathing system in this order: inspiratory valve, patient, expiratory valve, then CO2 canister. The other answers are incorrect, because they include parts of the anesthesia machine.
From the anesthesia machine gas flows as follows: Carrier gas exits the high pressure tank through the pressure-reducing valve, which maintains a steady gas pressure regardless of the pressure of the tank, and downregulates the variable high pressure in the tank down to 55-65 psi. From there it flows to the flowmeter. The pressure will be further downregulated to 14.5 psi by second pressure-regulating device just before the flowmeter.
It then flows through the flowmeter, which controls the amount of carrier gas delivered to the patient, then the vaporizer, where anesthetic vapor is produced from the liquid.
Anesthetic vapor carried by the carrier gas exits the vaporizer and flows into the breathing circuit for inhalation.
Exhaled gasses pass through a CO2 absorbent canister and are then rebreathed in a circle system, or are eliminated in a non-rebreathing system.
STRATEGY HINT: This is an ORDER question. If you already know that the CO2 canister is LAST in the order, you can narrow your choices down to two, right away. When you see ordering questions, look for things you are pretty sure must go FIRST or LAST, and then work from those choices to fill in between.
