Write a correct answer to the given question based on its associated fact. Make sure that your answer is contained in the associated fact. Don't be creative and introduce any new word that is not mentioned in the associated fact! Remember that the associated fact has been rearranged to form the question. So, the correct answer words must lie within the associated fact. The correct answer can be a word, phrase, or even a sentence.

Fact: claws are used to catch arthropods by some predators. 
Question: what do predators use claws to catch?
arthropods.

Fact: rivers can slowly dissolve carbon in sedimentary rock. 
Question: what can slowly dissolve carbon in sedimentary rock?
rivers.

Fact: a delta is formed by deposition of sand at the mouth of a river by water fanning out. 
Question: Deltas are formed by deposition of what at the mouth of a river by water fanning out?

sand.