input: Write a function to find the mode(s) of a given list using the Counter class from the collections module.
  assert find_mode([1,3,3,3,4,4,4,4,5,5]) == [4]
  assert find_mode([1,2,2,3,3]) == [2, 3]
  assert find_mode([7,8,8,9,9,9,10,10,10]) == [9, 10]
output: def find_mode(lst):
      from collections import Counter
      count = Counter(lst)
      max_freq = max(count.values())
      return [num for num, freq in count.items() if freq == max_freq]