C. Adverbs usually end in -ly and modify verbs.
Preposition is a word that indicates location so with that said....
pocket: I put the keys in my pocket (location)
bed: I put my shirt on my bed (location)
cushions: I set the vase down on the cushion (location?)
afternoon is a time. so the answer is afternoon
explaining why or how about your topic or saying goodbye to everybody I hope to see you soon.