In this task, you are given a sentence and question which can be answered using the sentence. Your task is to answer the question using the information from the sentence. The answer to the question is unique and it is a continuous text span from the sentence.
Example: Sentence: The album is named after the discredited pseudoscience of phrenology , the study of head shapes to determine intelligence and character , which was used to rationalize racism during the 19th century in the United States . 
 Question: what is  named  after something?
Example solution: The album
Example explanation: The output answers the question given as it is the album that is named after the discredited pseudoscience of phrenology. It is a continuous text span from the sentence and it does not use outside knowledge. Here the album is the answer that answers the what part of the question.

Problem: Sentence: An `` optical image stabilizer '' , often abbreviated OIS , IS , or OS , is a mechanism used in a still camera or video camera that stabilizes the recorded image by varying the optical path to the sensor . 
 Question: what   stabilizes something?

Show your work and conclude with the exact phrasing "Therefore, the final answer is [answer]." where [answer] is just the final number or expression that solves the problem.
user
Solution: a mechanism ### An `` optical image stabilizer '' ### An `` optical image stabilizer '' , often abbreviated OIS , IS , or OS ### a mechanism used in a still camera or video camera