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.