Question 20N.1.SL.TZ0.28

The graph shows a spirometer trace of oxygen consumption when breathing at rest and during exercise.

[Source: Courtesy of Dr. Dafang Wang for his work at University of Utah.]

What explains the difference between the traces at regions X and Y on the graph?

A. At X, the internal intercostal muscles contract more than the external intercostal muscles.

B. At Y, the ribcage moves up and out more than at X.

C. At X, the diaphragm flattens more per breath than at Y.

D. At Y, the intercostal muscles contract more slowly than at X.