he word "lesson" is a noun because it represents an idea or subject being taught. A noun names a person, place, thing, or idea. "Explained" is a verb indicating an action, "to" is a preposition showing direction, and "the" is an article modifying a noun. Other nouns in the sentence include "teacher" and "students," but since the question asks for a single noun, "lesson" is the correct choice. Learning to identify nouns helps in building better sentence structures and improving communication skills.