Explanation: The subject of a sentence is the person, place, thing, or idea that is performing the action. A complete verb includes the main verb and all of the helping verbs. To be considered a verb, it must describe a condition or an action and indicate tense. In the given sentence the subject is "you" and the complete verb is "have visited" where "have" is the helping verb and "visited" indicates the action.
Green roofs help reduce the Urban Heat Island Effect, a condition in which urban environments absorb and trap heat. A green roof's plants remove air particulates, produce oxygen and provide shade. ... Another important benefit of green roofs is their ability to reduce and slow stormwater runoff in urban environments
