The document discusses different types of if-clauses in English: - Zero conditional refers to general truths using present tense verbs in both clauses (e.g. "If you add two and two, you get four"). - Type one conditional expresses possible future events using present tense and "will" (e.g. "If she wins the next match, she will be world champion"). - Type two conditional refers to imaginary present situations using past tense and "would" (e.g. "If Mary were here, she would know what to do"). - Type three conditional expresses imaginary past events using past perfect and "would have" (e.g. "If he had asked