What do the rib muscles and diaphragm have in common? both aid in the expansion and relaxation of lungs. both produce red blood cells that carry oxygen. both filter air before it is delivered to the body’s cells. both deliver carbon dioxide to the surrounding muscle tissue.

The answer is that Both aid in the expansion and relaxation of lungs. Diaphragm and the rib muscles are vital in the breathing process. During inhalation the intercostal muscles contract, expanding the ribcage, the diaphragm contracts, pulling downwards to increase the volume of the chest, pressure inside the chest is lowered and air is sucked into the lungs. During exhalation the intercostal muscles relax, the ribcage drops inward and downwards, the diaphragm relaxes, moving back upwards, decreasing the volume of the chest, the pressure inside the chest increases and air is forced out. 

When you are making a guess you are forming a hypothesis