语句层次
　　六. It作形式主语时的常用句型
　　㈠形式一：It is+形容词+that/wh-从句
　　例：It is important_____________________(保持生态平衡)。
　　答案：that we should keep the balance of nature
　　(本题考查It 作形式主语时的用法，英语中的主语从句有时为了避免头重脚轻，常用it 作形式主语，而真正的主语用that引导放在后面)
　　㈡形式二：It+不及物动词+that…
　　例：He has been here only three days and
　　_______________________(由此可见他对那事一无所知)。
　　答案：it follows that he knows nothing about that
　　(本题考查 It+不及物动词+that…结构，注意前后句子时态的一致)
　　㈢形式三：It+be+名词+that…
　　例：It is our wish that__________________(他爱怎么样就怎么样)
　　答案：he does what he pleases
　　(本题考查 It作形式主语的同时，涉及了考试大虚拟语气的考查，在it is　our wish/hope that 等结构中，从句子的谓语动词要用should+动词原形这样的虚拟语气)
　　㈣形式四：It+be+done+that…
　　例：It is said that____________________(宇宙形成于一次大爆炸以后)
　　答案：the universe formed after the Big Explode
　　(本题考查 It作形式主语的用法，常用于It+be+done+that…，结构的动词有report, announce, expert等，常译为“据说”，“据报道”)
　　1.He told us not to wait for him because___________________(他是否来还不敢肯定)。
　　2.He has no intention of making progress so__________________(你老是帮助他是没有用的)
　　3.（后来证实）________________she is a friend of my sister.
　　4.Nevertheless,_________________(不可否认的是)，it can　bring some side-effects
　　答案：
　　1. it was uncertain whether he would come
　　2. it is no use that you always help him
　　3. It turned out that
　　4. it cannot be denied that