input: Write a function to perform matrix multiplication on two given matrices. If the matrices cannot be multiplied due to incompatible dimensions, return None.
  def matrix_multiplication(A, B):
      rows_A = len(A)
      cols_A = len(A[0])
      rows_B = len(B)
      cols_B = len(B[0])
      if cols_A != rows_B:
          return None
      result = [[0 for i in range(cols_B)] for j in range(rows_A)]
      for i in range(rows_A):
          for j in range(cols_B):
              for k in range(cols_A):
                  result[i][j] += A[i][k] * B[k][j]
      return result
  
  assert matrix_multiplication([[1, 2], [3, 4]], [[5, 6], [7, 8]])==[[19, 22], [43, 50]]
  assert matrix_multiplication([[1, 2]], [[3], [4]])==[[11]]
  assert matrix_multiplication([[1, 2, 3]], [[4], [5], [6]])==[[32]]
  assert matrix_multiplication([[1], [2], [3]], [[4, 5, 6]])==[[4, 5, 6], [8, 10, 12], [12, 15, 18]]
  assert matrix_multiplication([[1, 2]], [[3, 4], [5, 6], [7, 8]])==None
output: def matrix_multiplication(A, B):
      rows_A = len(A)
      cols_A = len(A[0])
      rows_B = len(B)
      cols_B = len(B[0])
      if cols_A != rows_B:
          return None
      result = [[0 for i in range(cols_B)] for j in range(rows_A)]
      for i in range(rows_A):
          for j in range(cols_B):
              for k in range(cols_A):
                  result[i][j] += A[i][k] * B[k][j]
      return result