input: Write a function to return a list of words that appear at least n times in the given list.
  from collections import Counter
  
  def frequent_words(words, n):
      counts = Counter(words)
      return [word for word, count in counts.items() if count >= n]
  
  assert frequent_words(['a', 'b', 'a', 'c', 'd', 'a', 'x', 'd', 'd'], 3) == ['a', 'd']
  assert frequent_words(['apple', 'banana', 'apple', 'orange', 'banana', 'apple'], 2) == ['apple', 'banana']
  assert frequent_words(['x', 'y', 'z'], 2) == []
  assert frequent_words([], 1) == []
  assert frequent_words(['one'], 1) == ['one']
output: 
  from collections import Counter
  
  def frequent_words(words, n):
      counts = Counter(words)
      return [word for word, count in counts.items() if count >= n]
  