input: Write a python function to split a sentence into words.
  assert get_words('This is a sentence.') == ['This', 'is', 'a', 'sentence.']
  assert get_words('Hello world') == ['Hello', 'world']
  assert get_words('Python is awesome') == ['Python', 'is', 'awesome']
output: def get_words(sentence):
      return sentence.split()