input: Write a function to return a list of words from a given list that appear at least n times. If no words appear at least n times, return an empty list. 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(['apple', 'banana', 'apple', 'apple', 'cherry', 'banana'], 2) == ['apple', 'banana']
  assert frequent_words(['one', 'two', 'three'], 4) == []
  assert frequent_words([], 2) == []
  assert frequent_words(['test', 'test', 'test', 'test'], 4) == ['test']
output: def frequent_words(words, n):
      from collections import Counter
      word_counts = Counter(words)
      return [word for word, count in word_counts.items() if count >= n]