input: Write a function to identify the longest word in a given sentence. If the sentence is empty, return an empty string.
  def find_longest_word(sentence):
      if not sentence:
          return ""
      words = sentence.split()
      longest_word = max(words, key=len)
      return longest_word
  
  assert find_longest_word("The rain in Spain stays mainly in the plain.") == "mainly"
  assert find_longest_word("Python is a versatile and powerful programming language.") == "programming"
  assert find_longest_word("") == ""
  assert find_longest_word("One two three four five") == "three"
  assert find_longest_word("This is a test sentence") == "sentence"
output: def find_longest_word(sentence):
      if not sentence:
          return ""
      words = sentence.split()
      longest_word = max(words, key=len)
      return longest_word