The best conclusion from the options provided is that "Prose poetry is written in complete sentences, while lyric poetry is not."
This is because prose poetry is characterized by its use of prose forms but retains poetic qualities like imagery and emotional resonance, blending the two styles. In contrast, lyric poetry typically relies on structured lines and stanzas rather than complete sentences and often expresses personal thoughts and feelings in a more fragmented form.
The other statements are inaccurate: both prose poetry and lyric poetry can use imagery and figurative language, and both can convey themes or messages. The defining characteristic between the two is the structure of the writing.