This document discusses conditional sentences in English. It provides examples of different types of conditional sentences:
- Second conditional sentences discuss impossible or unlikely present situations, using the structure "if + past tense, ...would..."
- Third conditional sentences discuss impossible past situations, using "if + past perfect, ...would have..."
- First/future conditional sentences discuss probable future events, using "if + present, ...will/going to..."
The document emphasizes there are four main types of conditional sentences: zero, first, second, and third conditionals. It provides examples and exercises to illustrate the different structures.