instruction:
Given scientific fact as input, generate the question from this fact such that it can be answered from the input.
question:
Some compounds form rigid frameworks called crystals.
answer:
Some compounds form rigid frameworks called what?


question:
Plasma membranes encloses and defines the borders of cells.
answer:
What encloses and defines the borders of cells?


question:
In the tropics tradewinds are the prevailing winds called.
answer:
In the tropics what are the prevailing winds called?