input: 
  from typing import List
  
  def predict_labels(data: List[List[float]]) -> List[str]:
      """ Predict the class labels of a given set of data.
      The dataset contains 4 features: Length, Width, Height, and Weight.
      The function should return a list of predicted labels for each data point.
      >>> predict_labels([[1.0, 2.0, 3.0, 4.0], [5.0, 6.0, 7.0, 8.0]])
      ['class1', 'class2']
      >>> predict_labels([[9.0, 10.0, 11.0, 12.0]])
      ['class3']
      """
  
output:     labels = []
      for point in data:
          length, width, height, weight = point
          if length < 3.0:
              labels.append('class1')
          elif length < 7.0:
              labels.append('class2')
          else:
              labels.append('class3')
      return labels