You are testing your anesthesia machine in the morning before cases begin. You disconnect the pipeline supply and turn on the backup oxygen cylinder to make sure it functions correctly. The oxygen cylinder is full and connected correctly, but the anesthesia machine still does not pressurize. You know that the problem could be due to a?
a) Faulty check valve
b) Empty vaporizer
c) Leak in the breathing circuit
d) Malfunctioning flowmeter