input: Write a python function to create a 20x20 matrix of zeros using NumPy.
  assert np.array_equal(create_zeros_matrix(), np.zeros((20, 20)))
  assert create_zeros_matrix().shape == (20, 20)
  assert create_zeros_matrix().sum() == 0
output: def create_zeros_matrix():
      import numpy as np
      return np.zeros((20, 20))