TASK DEFINITION: Given scientific fact as input, generate the question from this fact such that it can be answered from the input.
PROBLEM: Tornadoes can occur in any.

SOLUTION: At what time of the year can tornadoes occur?

PROBLEM: The active transport of ions across the membrane causes an electrical gradient to build up across the plasma membrane.

SOLUTION: The active transport of ions across the membrane causes an electrical gradient to build up across the what?

PROBLEM: Too little calcium can cause the disease osteoporosis.

SOLUTION:
What disease can too little calcium cause?