input: Write a python function to multiply two matrices.
  assert multiply_matrix([[1, 2], [3, 4]], [[1, 2], [2, 3]]) == [[5, 8], [11, 18]]
  assert multiply_matrix([[1, 0], [0, 1]], [[5, 5], [5, 5]]) == [[5, 5], [5, 5]]
  assert multiply_matrix([[2, 4], [3, 1]], [[1, 2], [0, 1]]) == [[2, 8], [3, 7]]
output: def multiply_matrix(A, B):
      result = [[0 for _ in range(len(B[0]))] for _ in range(len(A))]
      for i in range(len(A)):
          for j in range(len(B[0])):
              for k in range(len(B)):
                  result[i][j] += A[i][k] * B[k][j]
      return result