Which aspect of the following poem might imagists most admire?

Imagists believed that poems should have "no ideas but in things." In other words, they would described powerful images, and instead of explaining what those images meant, they would let the reader decide what the meaning or value of those images might be. 

Imagists were especially fond of inviting the reader to recognize how very different sorts of images can actually be really similar. Ezra Pound famously did this with his short poem "In a Station of the Metro," which associates "faces in the crowd" with "petals on a wet, black bough."

The poem in your question does something very similar by associating the cat's footprints in the snow with the blossoming flowers of a plum tree. The writer wants you to recognize the odd visual similarity of the footprints and the flowers, ideally to show how there's a kind of cosmic connectedness in the world by (because two very different things end up being really similar).

That's why I think your best answer is A.

The answer is A.) Marco rode to school on his bicycle this morning, he arrived an hour early.