instruction:
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?"
question:
Fact: tree squirrels generate heat mainly by keeping their metabolic rate high.
answer:
What generate heat mainly by keeping their metabolic rate high?


question:
Fact: digestive systems are needed to keep cells alive.
answer:
What do cells need to keep them alive?


question:
Fact: Viruses do not have walls and membranes.
answer:

What lacks walls and membranes?