Millions of years ago, the ancestors of giraffes had short necks and used to eat leaves from the bushes on the ground. A genetic mutation caused one giraffe's neck to be taller. This long-necked giraffe was able to eat leaves that were higher up on trees. This gave it an advantage as it was able to access more food than other giraffes. Over millions of years, all of the giraffes became long-necked. Which type of environmental factor caused this mutation to be inherited? (1 point)
polluted environment
radiation exposure
exercise requirement
food availability