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.
--------
Question: Fact: most bigger cities require vehicles. 
Question: What do most bigger cities require?

Answer: vehicles.


Question: Fact: paleontologists study the remains of plants. 
Question: What do palentologists study?

Answer: plants.


Question: Fact: negative feedback controls insulin secretion by what produces glucagon. 
Question: what controls insulin secretion by that which produces glucagon?

Answer:
negative feedback.