What is a light year? a. a measure of time in space b. the distance light travels in a year c. the distance to alpha centauri d. a term used only in science fiction

The term light year refers to the distance light travels in a year. 

A unit of astronomical distance equivalent to the distance that light travels in one year,

This is what i found on google “phytoplankton, tiny organisms that live in the ocean, are autotrophs. some types of bacteria are autotrophs. most autotrophs use a process called photosynthesis to make their food.” i hope this you for what your looking for