input: Write a function to identify and return a list of words that appear at least n times in a given list of words. If the given list is empty, return an empty list. The function should use the Counter class from the collections module to count the occurrences of each word.
  assert frequent_words(['a', 'b', 'a', 'c', 'd', 'a', 'x', 'd', 'd'], 3)==['a', 'd']
  assert frequent_words(['a', 'b', 'a', 'c', 'd'], 2)==['a']
  assert frequent_words(['x', 'y', 'z'], 1)==['x', 'y', 'z']
  assert frequent_words([], 3)==[]
  assert frequent_words(['a', 'a', 'a'], 4)==[]
output: from collections import Counter
  
  def frequent_words(words, n):
      if not words:
          return []
      word_counts = Counter(words)
      return [word for word, count in word_counts.items() if count >= n]