<h2>Right answer: It is used to measure long distances in space</h2>
A light year () is a distance unit that is approximately
.
By definition it is <em>the distance that a photon would travel in vacuum during a Julian year (365.25 days) at the speed of light (299 792 458 m/s) at an infinite distance from any gravitational field or field magnetic. </em>
<em> </em>
In other words:
It is the distance that light can travel in a year.
This unit is used to measure large distances in space. Therefore the correct answer is D.