modal verb + be 后 + of

請看以下兩句：

As a good student, living up to the expectation from parents and teachers may be their top priority.

As a good student, living up to the expectation from parents and teachers may be of top priority.

兩句都是正確的，關鍵在於 "their"。第一句解 living up to the expectation from parents and teachers 就是學生的首要考慮。
living up to the expectation from parents and teachers = top priority

第二句解 living up to the expectation from parents and teachers 屬於首要考慮。

再看以下兩句：
The agreement between them is their top secret.
他們中間的恊議是他們最大的秘密。
The agreement between them is of top secret to them.
他們中間的恊議屬他們最大的秘密。

of + 屬形容詞的抽象名詞
of + 形容詞 + 名詞
是 adjective phrase.

所以是否需要 of 是看 be 後的片語是主詞的等同還是對主詞的形容。

以下句子中的 of 都有 possessing certain quality (有某種特質) 的意思：

He is a man of great ability.
She is a woman of great determination.
People of different persuasions cannot work together. (不同信念的人不能共事。)

將這三句用 relative clause 寫出來就成為：
He is a man who is of great ability.
She is a woman who is of great determination.
People who are of different persuasions cannot work together.

is + of 後面是名詞，有/屬於某種特質 的意思，of 不能省去。
其他 is + of + 名詞 的例子：

This operation is of great importance to the safety of the country.
Protecting the computers against intrusion is of the highest priority for the IT people.
This treaty between the two countries is of great political significance.
Web sites that are of obscene nature are blocked by our server.



2012-01-27 07:19:08 補充：
Compare to:
Protecting the computers against intrusion is the highest priority of the IT people.
Protecting the computers against intrusion 就是 the highest priority.

Asa good student, living up to the expectation from parents and teachers may be their top priority le句唔使 be of.佢純粹係話符合家長同老師既期望是首要目的,而唔係話符合家長同老師既期望是有首要目的，所以從字面上就解得通。
be +of sth(noun phrase).其實係= contain(含有) sth.
eg 1. Your information provided should be [of interest]= interesting to the readers.
你所提供給讀者的資料應是有趣味的.--->be of interest(n.) 即含有趣味性；be interesting(adj.) 即有趣的。意思係相通既
eg 2. The policy is [of utmost(adj) importance(n.)]= important in coping with the current flaws in the society.這個政策對於解決社會現有的缺陷是很重要的/這個政策對於解決社會現有的缺陷是有相當的重要性
明唔明白？即係 1.是..同2.含有xx性的分別！

(grammar)a verb such as can,may should or will that is used with another verb(not a modal) to express possibility,permission,intention,etc.
have found your eg:-A good student(subj)
may be (verb,or modal verb)
whereas should be is auxiliary verb,
In your eg.:- (Maintaining the living standard---for you) ,(gerund+subject)
should be (verb,or modal verb)
(of top priority means a top priority), (adv.phr)