I need help on this which word is vague in this sentence

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. a. poetry should be about urban subjects and ideas. b. old poetry should be rewritten in a modern style. c. poets should be able to describe ordinary subjects in new ways. d. poets should write about new subjects with conventional techniques.