input: Write a python function to classify numbers as 'low' or 'high' based on a given threshold.
  assert classify([8, 5, 9, 1, 3, 10]) == ['high', 'low', 'high', 'low', 'low', 'high']
  assert classify([6, 4, 7, 2, 3, 11]) == ['high', 'low', 'high', 'low', 'low', 'high']
  assert classify([5, 5, 5, 5, 5, 5]) == ['low', 'low', 'low', 'low', 'low', 'low']
output: def classify(numbers, threshold=5):
      return ['high' if num > threshold else 'low' for num in numbers]