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

[EX Q]: Acid changes the shade of certain paper at different acidity.
[EX A]: What does acid change the shade of paper at?

[EX Q]: a thinning and weakening of bone is an affliction in which osteoclasts are more active than osteoblasts
[EX A]: What are more active than osteoblasts?

[EX Q]: A bill is used to catch prey by some ducks.
[EX A]:
Who uses a bill to catch prey?