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

Input: Consider Input: A concave lens is thicker at the edges than it is in the middle.

Output: What type of lens is thicker at the edges than it is in the middle?

Input: Consider Input: Volvox sphere has a distinct front and back end.

Output: What has a distinct front and back end?

Input: Consider Input: Mantle is the layer of tissue between the body and shell.
Output: What is the layer of tissue between the body and shell called?