Which of the following words is a preposition? over quickly it however

Which is the most engaging way of describing how to prevent eyestrain? o a. the medical term for eyestrain is asthenopia, and is caused by the contraction of the ciliary muscle. o b. to prevent eyestrain, people should not look at screens for as long as they often do. o c. the human eye tires after staring at close objects, such as computer monitors, for too long. o d. remember the 20/20/20 rule: every 20 minutes, look at something 20 feet away for 20 seconds