input: Write a python function to find the longest word in a given sentence.
  assert find_longest_word('This is an example sentence with some words.') == 'sentence'
  assert find_longest_word('The quick brown fox jumps over the lazy dog.') == 'jumps'
  assert find_longest_word('A journey of a thousand miles begins with a single step.') == 'thousand'
output: def find_longest_word(sentence):
      words = sentence.split()
      longest_word = max(words, key=len)
      return longest_word