[解析] 这是一个典型的虚拟语气的题目，与过去事实相反的虚拟语气结构为：从句用 “had + 过去分词”，主句用 “would/could/should/might + have + 过去分词”。 在本题中，正常语序应该是 “If he had left last Friday, he would have got to Paris.”，当把 if 省略时，就需要把 had 提到主语前面进行倒装，变成 “Had he left last Friday, he would have got to Paris.”