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: when rivers slow, sediment is dropped at the mouth of a river by water.
Sediment is dropped at the mouth of a river by water when what happens?

Fact: Friendship often comes before mating.
What often precedes mating?

Fact: chemical weathering causes iron in limestone to oxidize.

chemical weathering causes iron to oxidize in what?