PLEASE HELP! Which statement is true?

-A translation is a function becuase a translation vector is always horizontal.
-A translation is a function because each point on the pre-image in mapped to a unique point on the image.
-A translation is not a function becuase the image could overlap the pre-image.
-A translation is not a function becuase a point on the pre-image could be mapped to more than one pointon the image.