input: Write a function that takes a list of words and an integer n and returns a list of words that appear at least n times in the given list. If the list is empty return an empty list. The function should use the Counter class from the collections module to efficiently count word occurrences.
  assert frequent_words(['a', 'b', 'a', 'c', 'd', 'a', 'x', 'd', 'd'], 3)==['a', 'd']
  assert frequent_words(['a', 'b', 'c'], 2)==[]
  assert frequent_words([], 1)==[]
  assert frequent_words(['a', 'a', 'b', 'b', 'b', 'c', 'c'], 2)==['a', 'b', 'c']
  assert frequent_words(['x', 'y', 'z'], 1)==['x', 'y', 'z']
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]