Given scientific fact as input, generate the question from this fact such that it can be answered from the input.
One example: Earth rotates on its axis once times in one day.
Solution is here: How many times does Earth rotate on its axis in one day?
Explanation: The given output correctly poses a question based on the scientific fact given.

Now, solve this: Iguassu falls is the largest waterfall on the planet.
Solution:
Which waterfall series is the largest on the planet?