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.
The 'underground railroad' was known as such due to the slaves using it to escape and the people helping them to escape using secret codes that were commonly associated with railroads.
(Ex: 'station masters' = people who would hide slaves)
