input: Write a python function to find the most frequent element in a list.
  assert most_frequent_elements([3, 4, 2, 5, 4, 3, 2, 5, 4]) == 4
  assert most_frequent_elements([1, 2, 3, 1, 2, 1, 1]) == 1
  assert most_frequent_elements([7, 8, 9, 8, 8, 7, 9, 9, 9]) == 9
output: def most_frequent_elements(lst):
      from collections import Counter
      count = Counter(lst)
      return count.most_common(1)[0][0]