input: Write a python function to multiply two matrices.
  assert multiply([[1, 2], [3, 4]], [[5, 6], [7, 8]]) == [[19, 22], [43, 50]]
  assert multiply([[2, 0], [1, 2]], [[1, 2], [3, 4]]) == [[2, 4], [7, 10]]
  assert multiply([[1, 2, 3], [4, 5, 6]], [[7, 8], [9, 10], [11, 12]]) == [[58, 64], [139, 154]]
output: def multiply(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