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]], [[2, 0], [1, 2]])==[[4, 4], [10, 8]]
  assert matrix_multiplication([[1, 2]], [[1], [2]])==[[5]]
  assert matrix_multiplication([[1, 2]], [[1, 2, 3], [4, 5, 6]])==None
  assert matrix_multiplication([[1, 2, 3], [4, 5, 6]], [[1, 2], [3, 4], [5, 6]])==[[22, 28], [49, 64]]
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
  