Answer: Sun-dried tomatoes
Explanation: This is the only case in which a noun (sun) is joined to a past participle verb (dried) to form an adjective, which in this case means "dried in the sun." In "cold, damp weather" and "old, worn sofa" a comma should be used instead (we are stacking adjectives that modify a same noun), whereas no punctuation is advised in "bright green leaves," provided bright is acting as an adverb that modifies green.
