input: Write a python function to search for an animal in a list of animals and return it if found.
  assert search_animals("cat") == "cat"
  assert search_animals("dog") == "dog"
  assert search_animals("elephant") == None
output: def search_animals(animal):
      animals = ["cat", "dog", "mouse", "bird", "fish"]
      if animal in animals:
          return animal
      return None