This document discusses conditional sentences in English. There are three types of conditional sentences: real, present unreal, and past unreal. Real conditional sentences use the present simple tense to refer to possible future events. Present unreal conditional sentences use the past tense to talk about imagined present situations. Past unreal conditional sentences use the past perfect tense to describe impossible past events. The document provides examples of each type of conditional sentence and exercises for the reader to practice forming conditional sentences.