input: Write a python function to generate a dictionary that keeps count of how many times each word appears in a given sentence.
  assert count_words("the quick brown fox jumps over the lazy dog") == {'the': 2, 'quick': 1, 'brown': 1, 'fox': 1, 'jumps': 1, 'over': 1, 'lazy': 1, 'dog': 1}
  assert count_words("hello hello world") == {'hello': 2, 'world': 1}
  assert count_words("test test test test test") == {'test': 5}
output: def count_words(sentence):
      words = sentence.split()
      word_count = {}
      for word in words:
          if word in word_count:
              word_count[word] += 1
          else:
              word_count[word] = 1
      return word_count