What ideal of imagist poetry is best reflected in this poem by Ezra Pound in which he compares a crowded metro station to a flowering tree branch?

In a Station of the Metro
The apparition of these faces in the crowd;
Petals on a wet, black bough.

Poetry should be about urban subjects and ideas.
Old poetry should be rewritten in a modern style.
Poets should be able to describe ordinary subjects in new ways.
Poets should write about new subjects with conventional techniques.