Given scientific fact as input, generate the question from this fact such that it can be answered from the input.

[Q]: A concave lens is thicker at the edges than it is in the middle.
[A]: What type of lens is thicker at the edges than it is in the middle?


[Q]: The long bone work as lever.
[A]: What type of function does the long bone perform?


[Q]: The vascular structure functions as a framework that reinforces the shape of the leaf.
[A]:
What functions as a framework that reinforces the shape of the leaf?