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?"

[Q]: Fact: Bacteria can cause bodily tissues to swell.
[A]: Bacteria can cause what?


[Q]: Fact: PDAs require electrical energy to function.
[A]: What requires electrical energy to function?


[Q]: Fact: Immunodeficiency occurs when the immune system is broken down.
[A]:
Immunodeficiency occurs when the immune system is what?