After Accounting for the Compressed Volume Loss on a Stable

After accounting for the compressed volume loss on a stable adult patient receiving volume-controlled continuous mandatory ventilation at a preset volume of 500 ml, you still note a 150-ml difference between the expected and the actual delivered volume. Which of the following is most likely causing this problem?

A) Gas absorption across the alveolar membrane
B) Increase in the respiratory quotient
C) Bronchopleural fistula or pneumothorax
D) Leak in the patient-ventilator system