Turn the given fact into a question by a simple rearrangement of words. This typically involves replacing some part of the given fact with a WH word. For example, replacing the subject of the provided fact with the word "what" can form a valid question. Don't be creative! You just need to rearrange the words to turn the fact into a question - easy! Don't just randomly remove a word from the given fact to form a question. Remember that your question must evaluate scientific understanding. Pick a word or a phrase in the given fact to be the correct answer, then make the rest of the question. You can also form a question without any WH words. For example, "A radio converts electricity into?"

Fact: Water must not be polluted to be safe.
What can happen to water to make it unsafe?

Fact: milk helps to repair cells in the human body.
Milk helps to?

Fact: a planet rotating determines that we work in the day and sleep at night.

Sleeping at night and working during the day is determined by what thing happening?