The correct answer is A. lunches and river.
A common noun is concrete - it refers to something you can touch, feel, something that surrounds you; words such as desk, mirror, rug, are all common nouns.
B is incorrect because those are proper nouns, meaning they refer to the names of people or places. C is incorrect because eat is a verb, and side is an abstract noun. D is incorrect because both words are verbs.
