Given a statement, generate a question such that the answer is contained in that statement.

[Q]: eagles steer by using muscles in their chest
[A]: Who steers by using muscles in their chest?

[Q]: jaws make sharks excellent predators
[A]: What makes sharks excellent predators?

[Q]: Pigeon eggs have hard shells made of calcium carbonate.
[A]:
What is the hard shell of pigeon eggs made of?