input: Write a python function to extract words with four or more characters from a sentence.
  assert words_with_four_or_more_characters("This is a test sentence") == ["This", "test", "sentence"]
  assert words_with_four_or_more_characters("Python programming is fun") == ["Python", "programming"]
  assert words_with_four_or_more_characters("Hello world") == ["Hello", "world"]
output: def words_with_four_or_more_characters(sentence):
      return [word for word in sentence.split() if len(word) >= 4]