Ever since the reform and opening-up, China has made great achievements in its social and economic development, which have won worldwide recognition.
Yet, it is obvious that its social development is lagging behind that of its economy.
【正确答案】但一个明显的事实是，同经济发展相比，社会发展明显滞后。
【答案解析】 原句是主从复合句，it是逻辑主语，真正的主语是that引导的主语从句。behind that of its economy中的that代指development，英语中为避免重复，常用代词代替上文已经出现的事物。汉译时，“经济发展”前置，可起到强调作用，也使句子更通顺。