Answer: the distance light travels in one year
Explanation: A light year is the distance light travels in one year. Option 2 is incorrect because light only takes about 8.3 minutes to reach Earth from the sun (appx 1.5781e-5 Light years), instead an astronomical unit (au) measures the distance between the Earth and the Sun. The last option is incorrect because light doesn't "burn out" only after 1 year (although it does lose energy over time).