input: Write a function to perform matrix multiplication on two given matrices. The function should return the resulting matrix after performing the multiplication. If the matrices cannot be multiplied, 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, 0], [0, 1]], [[1, 2], [3, 4]]) == [[1, 2], [3, 4]]
  assert matrix_multiplication([[1, 2, 3], [4, 5, 6]], [[7, 8], [9, 10], [11, 12]]) == [[58, 64], [139, 154]]
  assert matrix_multiplication([[1, 2]], [[1], [2]]) == [[5]]
  assert matrix_multiplication([[1, 2, 3]], [[1], [2]]) == 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