code: #!/usr/bin/env python3
  import numpy as np
  matrix = np.array([[1, 2, 3, 4, 5, 6], [7, 8, 9, 10, 11, 12],
                     [13, 14, 15, 16, 17, 18], [19, 20, 21, 22, 23, 24]])
  mat1 = matrix[1:3]
  mat2 = matrix[:, 2:4]
  mat3 = matrix[1:, 3:]
  print("The middle two rows of the matrix are:\n{}".format(mat1))
  print("The middle two columns of the matrix are:\n{}".format(mat2))
  print("The bottom-right, square, 3x3 matrix is:\n{}".format(mat3))
  
apis: numpy.array