increasing the pressure inside the wings decreasing the density of the wings increasing the temperature inside the wings decreasing the mass of the wings
I gave my students this multiple choice question: When a butterfly emerges from its chrysalis, its wings are crumpled. In order to expand its wings, the butterfly hangs upside down, causing fluid to be pumped into the veins of its wings. This pumping most likely expands the wings by

Only one answer is correct among these 4 choices:
- increasing the pressure inside the wings
- decreasing the density of the wings
- increasing the temperature inside the wings
- decreasing the mass of the wings

Could you tell me which one is correct?

increasing the pressure inside the wings