It is believed that the couple have left the country. 

据信那对夫妇已经离开了这个国家。

【答】这个句子的主动式应该为：

People believe that the couple have left the country. 

人们认为，那对夫妇已经离开了这个国家。

没想到，《牛津高阶英语词典》第 7 版的中文翻译很蹩脚。“据信”二字，跟本句的意思严重脱离。即便翻译成“相信”，也应说“人们相信”。believe 接宾语从句时，表示人的观点、看法，应该译成“认为”。估计是模仿It is said that...（据说......）的结果。

大家可以查查“据信”是什么含义吧。查阅《现代汉语大辞典》，“据信”有3种含义：

1. 据信：即“拒信”，一般泛指在提交个人简历至用人单位后，用人单位返给的不予录用的书面通知。

2. 据信：根据相关信息。

3. 据信：据说可以相信。

在这3个意思中，前两个意思肯定不通，第3个意思“据说可以相信”与本句的意思仍然不符。

以下两句，意思相同吗？

1. 据说可以相信，那对夫妇已经离开了这个国家。

2. 人们认为，那对夫妇已经离开了这个国家。

一般而言，“It + be + 过去分词 + that从句”就是下句S + V + Object Clause 的变式：

People believe that the couple have left the country. 

= It is believed that the couple have left the country. 

人们认为，那对夫妇已经离开了这个国家。

又如：

It is said that the professor has already succeeded in carrying out this experiment.

据说这位教授已经成功地完成了这项实验。

It is believed that Indians were the first settlers in the Americas.

人们认为印第安人是美洲的第一批移民。

It is reported that more than thirty miners were buried in the mine.

据报道30多位矿工被埋矿中。

It is generally considered that women live longer than men.

人们普遍认为女人比男人长寿。

常见的这类结构有：

It is said that  据说 

It is told that  有人告知

It is heard that  听说

It is reported that  据报道     

It is decided that  已经决定   

It is suggested that  有人建议

It is advised that  有人建议   

It is ordered that  根据命令   

It is remembered that  人们记得

It is thought that  有人认为   

It is considered that  大家认为     

It is hoped that  人们希望

It is expected that  人们预料 

It is announced that  已宣布

It is believed that  大家认为

It is found out that  经查明   

It is pointed out that 有人指出     

可以肯定的说：believe 没有 “tell sb. that 从句”这个类似的用法和句式。believe 不能接双宾语，只能接单宾语（由名词、代词充当，或由that 从句充当）。

It is believed that the couple have left the country. 这个句子是下面这个句子结构变来的。

People（主） believe （谓）that the couple have left the country.（宾） 

→That the couple have left the country is believed by people.（把宾语当主语）

→That the couple have left the country is believed. （by people 可以省略不说）

→It is believed that the couple have left the country. （用形式主语It 替换that 从句，把that 从句放在句末）