17、…是必要的：It is necessary that S（should）V

…是重要的：It is important/essential that S（should）V

…是适当的：It is proper that S（should）V

…是紧急的：It is urgent that S（should）V

例︰我们当保持公共场所清洁是应当的。

It is proper that we（should）keep the public places clean.

18、每当我听到…我就忍不住感到兴奋。

Whenever I hear…，I cannot but feel excited.

每当我做…，我就忍不住感到悲伤。

Whenever I do…，I cannot but feel sad.

每当我想到…，我就忍不住感到紧张。

Whenever I think of…，I cannot but feel nervous.

每当我遭遇…，我就忍不住感到害怕。

Whenever I meet with…，I cannot but feel frightened.

每当我看到…，我就忍不住感到惊讶。

Whenever I see…，I cannot but feel surprised.

例︰每当我想到我家附近那一条清澈的小溪？我就忍不住感到悲伤。

Whenever I think of the clean brook near my home，I cannot but feel sad.

Every time I think of the clean brook near my home，I cannot help feeling sad.

19、据说…

It is said（that）子句

一般认为…

It is thought（that）子句

大家都知道…

It is known（that）子句

据报导…

It is reported（that）子句

一般预料…

It is expected（that）子句

一般估计…

It is estimated（that）子句

一般相信…

It is believed（that）子句

例︰一般相信阅读增加我们的知识、扩大我们的心胸。

It is believed（that）reading increases our knowledge and broadens our mind.

20、…的主要理由是…

The main reason why…is（that）子句

例︰青少年犯罪的主要理由是社会环境日一败坏。

The main reason why the juveniles commit crimes is that social environment is becoming worse.

21、俗语说得好…

Well goes an old saying…

As an old saying goes（runs，says）…

An old saying goes…

It's an old saying（that）子句

例︰俗话说得好：“诚实为上策”。

As an old saying goes，“Honesty is the best policy.”

22、（A）…用下列方法…

…in the following ways.

（B）…有三个主要理由。

…for three major reasons.

（C）要…至少我们可做三件事。

To…，there are at least three things we can do.

例︰（A）我用下列方法增加信心。

I increase my confidence in the following ways.

（B）人们学外语有三个理由。

People learn a foreign language for three major reasons.

（C）为了维护健康，我们每天至少可做三件事。

To keep healthy，there are at least three things we can do every day.