The bottom line requires that the numbers corresponding to "Five" should be inserted in the bottom line respectively, so that no matter what numbers are, they must be higher or lower than "Five", and the words inserted (such as "Qiantang River Bridge") cannot correspond to each other one by one, and the four words inserted must be radical.
Of course, the five elements can also be used to correspond to the five elements, but the upper and lower couplets cannot be completely opposite, so they are not neat.