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: vein deposits of gold and silver are formed by granite.
what are vein deposits of gold and silver formed by?

Fact: Octopuses spray a cloud to hide from predators.
Octopuses spray a cloud to hide from what?

Fact: fossil fuels are used for generating heat by burning.

What is used for generating heat by burning?