input: Write a python function to split a sentence into words.
  assert split_into_words("This is a test sentence") == ["This", "is", "a", "test", "sentence"]
  assert split_into_words("Another example sentence here") == ["Another", "example", "sentence", "here"]
  assert split_into_words("OneWord") == ["OneWord"]
output: def split_into_words(sentence):
      return sentence.split()