input: Write a python function to segment a sentence into words using the split() method.
  assert segment_sentence("This is a sentence.") == ["This", "is", "a", "sentence."]
  assert segment_sentence("Python is great!") == ["Python", "is", "great!"]
  assert segment_sentence("Hello, world!") == ["Hello,", "world!"]
output: def segment_sentence(sentence):
      return sentence.split()