This document discusses the four types of conditional sentences in English. It provides examples and structures for each type, as well as exercises for the reader to practice each type. Conditional type 0 is used to talk about general truths and facts. Conditional type 1 is used to talk about real possibilities in the present or future. Conditional type 2 is used to talk about imaginary or unreal situations in the present. Conditional type 3 is used to talk about situations that happened in the past that cannot be changed. The document provides detailed explanations and examples of when and how to use each type of conditional sentence.