input: Write a function to classify nouns as 'Animal', 'Vehicle', or 'Unknown' based on provided lists of animal and vehicle words.
  assert classify('dog') == 'Animal'
  assert classify('car') == 'Vehicle'
  assert classify('elephant') == 'Unknown'
output: def classify(noun):
      animals = ['dog', 'cat', 'elephant', 'lion']
      vehicles = ['car', 'bike', 'truck', 'bus']
      
      if noun in animals:
          return 'Animal'
      elif noun in vehicles:
          return 'Vehicle'
      else:
          return 'Unknown'