input: Write a function to find and print the top 5 most frequent words in a given sentence. If the sentence is empty, return an empty list. 
  
  assert most_frequent_words("Python is an interpreted, high-level, general-purpose programming language.") == [('Python', 1), ('is', 1), ('an', 1), ('interpreted,', 1), ('high-level,', 1)]
  assert most_frequent_words("") == []
  assert most_frequent_words("a a a b b c") == [('a', 3), ('b', 2), ('c', 1)]
output: def most_frequent_words(sentence):
      if not sentence:
          return []
      words = sentence.split()
      freq = {}
      for word in words:
          if word in freq:
              freq[word] += 1
          else:
              freq[word] = 1
      sorted_words = sorted(freq.items(), key=lambda x: x[1], reverse=True)
      return sorted_words[:5]