关于There be 的这种特殊用法，可以按着以下思路去理解和把握：

▲我们知道，there be 句型可有各种非谓语形式。例如：

I don’t want there to be any misunderstanding. 我可不希望有任何误解。

It was too late for there to be any buses. 太晚了，不会有公共汽车了。

There being nothing to do, I went to bed. 因为没事可做，所以我就上床睡觉了。

What’s the chance of there being an election this year? 今年举行选举的可能性有多大?

以上说明：There be 句型中，可以有不定式there to be，现在分词 there being 以及动名词there being 等形式。

▲下面3个句子，是我们经常见到的句式转换，而意思保持不变：

A. People say that he is one of the most important scientists in history.

B. → It is said that he is one of the most important scientists in history.

C. → He is said to be one of the most important scientists in history.

▲据此，从理论上讲，there be 句型如果充当了某个及物动词（如：say）的宾语从句，那么，这个及物动词，就可以用于上述句式的转换。例如：

1. People say that there will be an election this week.

→ It is said that there will be an election this week.

→ There is said to be an election this week.

（注意：不定式本身就表示将来，所以will 不再出现，不能说：There will be said to be）

2. The media report that there is oil under that desert.

→It is reported that there is oil under that desert.

→There is reported to be oil under that desert.

3. People expect that there will be a keen fight in the local elections.

→It is expected that there will be a keen fight in the local elections.

→There is expected to be a keen fight in the local elections.

以上说明：There be 句型可以理解为有被动式。

▲并非所有接宾语从句的及物动词，都可以用于该句式。据我所知，具有该用法的动词只是有限的一小部分，如：say, report, expect, think, believe, suppose, understand 等。

1. There is/are said to be... 据说有......

2. There is/are reported to be... 据报道有......

3. There is/are expected to be... 预计有......

4. There is/are thought to be... 人们认为有......

5. There is/are believed to be... 人们认为有......

6. There is/are supposed to be...人们认为有......

7. There is/are understood to be... 人们都知道有......

下面，我再把网友给出的这两个句子，分别转换一下：

1. People think that there will be a strike soon.

→It is thought that there will be a strike soon.

→There is thought to be a strike soon.

2. People think that there are more than 3000 languages in the world.  

→It is thought that there are more than 3000 languages in the world. 

→There are thought to be more than 3000 languages in the world.  

▲下面是我在语料库 Corpus of Contemporary American English (COCA) 查到的There is/are thought to be 的例句：

1. There are thought to be half a million people displaced by the war throughout Eritrea.
2. There are thought to be about four thousand such funds.
3. If there are imperfections in the speech market, well, there are thought to be far greater dangers in having government be the regulator of speech.
4. But still there are thought to be serious obstacles to penetrate in Japan's market and that discourages foreign importers.
5. Altogether, there are thought to be pools scattered across as many as 8,000 acres on the base.
6....standard of persuasion " is reserved for special types of claims " where there is thought to be special danger of deception, or where the court thinks the particular type.
7. SIMON: There is thought to be significance in the fact that the president begins his trip in Poland.
8. There is thought to be such a subsurface ocean on Jupiter's moon Europa.
9....and besides if there is thought to be grounds, do you really need to subpoena him again to get more.