input: Write a function to find the most frequent word in a sentence using collections.Counter.
  assert most_frequent("Python is a powerful language that is used for a wide range of applications") == ('is', 2)
  assert most_frequent("this is a test and this test is just a test") == ('test', 3)
  assert most_frequent("to be or not to be that is the question") == ('to', 2)
output: def most_frequent(sentence):
      from collections import Counter
      
      words = sentence.split()
      frequency = Counter(words)
      most_common_word, count = frequency.most_common(1)[0]
      
      return (most_common_word, count)