John is short is public knowledge. 这就错了，因为有两个谓语动词。
That John is short is public knowledge .(有点拗口却完全正确）
It is public knowledge that John is short.
That the seas are overfished has been known for years.
It has been known for years that the seas are overfished.
It is a pity that we won’t be able to go to the south to spend our summer vacation.
It is no woder that he has accomplished so much in such a short time – he has learned from the best.(不奇怪）
It is obvious(true/clear/fortunate)that+主语+动词
It is obvious that we were all tricked by him.|很显然我们被他捉弄了。
It is fortunate that no one got hurt.|很幸运没人受伤。
It is necessary(strange,important,possible,wonderful…)that+主语+should do…
It is important that we all should attend the meeting.
It is strange that the man should stick to his silly ideas.|他要坚持他自己愚蠢的想法真是奇怪。
It is doubtful whether he’ll be able to come.=Whether he will be able to come is doubtful.
It is likely that…有可能（这个句型很好用）
It is likely that investors will face losses.|投资者很可能会赔钱。
It is likely that they would go into hiding for a few weeks,and resurface when the publicity has died down.
3)It + be + 动词的过去分词 +that从句
It is said(reported,decided,found,believed,thought…)+that从句。
It is reported that nearly 2/3 of the voters are planning to vote for Mr.Johnson.
It is believed that health is above wealth. 大家都相信健康高于财富。
4)It + 不及物动词+that从句
It seems(happened,doesn’t matter,has turned out,…)that.
It has turned out that none of us were correct. 结果是我们都不对。
It happened that I ran out of money.我碰巧没有钱。
It seems certain that….（……看起来很肯定的）
It remains a secret that…(……还是个秘密）
It occurs to sb.that…
It dawns on sb.that…某人想起什么事情。
It occurred to me that I could use my husband’s credit card instead of mine.我想起来我可以用我老公的信用卡。
It occurred to him that he had forgotten to lock the door when he left home.
He’s just not that into you…
I was dating a guy for a couple of months when it suddenly dawned on me that he didn’t seem particularly excited about me.
That John is short is public knowledge. 正确(有引导词)
Why John is short is public knowledge. 从句有引导词，也正确。
What I need is money.
What he says is not important.
What make the river more beautiful are the lotus plants growing in the water.让河流更漂亮的是生长在水里的莲花。
What doesn’t kill you makes you stronger.
How I spend money is none of your busines.
Whoever comes fisrt will recive the prize.
I am sure that what she said is wrong.
What we all need is a spell of warm sunshine.
What is troubling me is that I don’t have much experience in international commerce.让我困扰的事情是…
Whether we can trust him(or not) is still unclear.
Whether 引导主语从句也经常用it 作形式主语：
It is unclear whether we can trust him(or not).
Just because…doesn’t mean…
Just because we don’t talk doesn’t mean I don’t think about you .我们不说话并不代表
Just because we can’t be together doesn’t mean I won’t love you .我们不在一起并不代表
Just because you like it doesn’t mean I will.你喜欢它并不意味着我喜欢它。