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: Atolls are built by corals secreting an exoskeleton.
answer:
How are atolls built?


question:
Fact: The production of heat occurs when many muscles contract a little bit all at once.
answer:
What occurs when many muscles contract a little bit all at once?


question:
Fact: Veins carry blood that's heavy with carbon dioxide.
answer:

What does blood in the veins have a lot of?