I want to know the answer to the following question:
How many large flight muscles do birds have?
All the background I'm provided with is that "Birds have various adaptations for flight, including a lightweight skeleton, two large flight muscles, the pectoralis (which accounts for 15% of the total mass of the bird) and the supracoracoideus, as well as a modified forelimb (wing) that serves as an aerofoil.". Is that enough to answer the question?