Max is comparing the poems'

kigo

moods

rhythms

structures

D. Structures

Explanation:

In his paper contrasting a haiku and the poem "Ozymandias", Max wrote this statement;

One way the poems differ is that the haiku is organized into three fixed lines, while "Ozymandias" has fourteen lines.

Max is comparing the poems' structures.

The structure of a poem refers to the way it is presented to the reader. This could include technical things such as the line length and stanza format. Also, line length shows the reader how it should be read.