The best choice is option C. A conceit is an "extended metaphor" - meaning it is drawn out or lengthy, possibly even explored throughout the entire poem. Another characteristic of a conceit is that it is often a surprising unexpected comparison - for example, comparing two things that are not at all related - which may help the author of the poem to more effectively grab the reader's attention.
An example of a conceit in poetry includes Shakespeare’s well-known sonnet, Sonnet 18, which begins “Shall I compare thee to a summer’s day?” Throughout the poem, the subject (the person the narrator is talking about) is compared to a summer's day, making this an extended metaphor.
