Final answer:
If only the external intercostal muscles contracted, the rib cage would expand, causing inhalation, but the expiration process would be affected because the internal intercostal muscles are responsible for constricting the rib cage during expiration.
Step-by-step explanation:
The external intercostal muscles play a role in inspiration by raising the rib cage, which expands it and increases the volume inside the pleural cavities. This decrease in pressure within the pleural cavities allows air to flow into the lungs. If only the external intercostal muscles contracted, the rib cage would expand, leading to inhalation, but the expiration process would be affected because the internal intercostal muscles are responsible for drawing the ribs together to constrict the rib cage during expiration.