If you describe someone as la-di-da, you mean that they have an upper-class way of behaving, which you think seems unnatural and is only done to impress people.

【参考译文】如果你把某人描述成为装模作样的人，你的意思是说他们故意表现出上流人士的姿态，你认为似乎不自然的而且其目的仅仅使人印象深刻.

请问：如何分析与理解粗体部分的从句呢？

回答如下：

黑体字语法结构分析如下

关系代词引导非限制性定语从句:which

插入语：you think （你认为）

系动词：seems（似乎/好像）

表语：unnatural（不自然的，做作的）

连词：and（而且，以及）

并列谓语：is done to impress people（这样做目的使人印象深刻）

(备注：并列谓语前省略主语(which) is done to impress people

几个单词及短语补充解释如下：

【1】la-di-da 有以下词性及意思

(1)adj. 装模作样的；做作的

(2)n. 装模作样的人

I wouldn't trust them in spite of all their la-di-da manners.

尽管他们处处显得很高雅的样子，我还是不相信他们。

【2】unnatural 

(1)adj.不自然的；诡异的；反常的

The aircraft rose with unnatural speed on take-off.

那架飞机以反常的速度起飞升空。

The altered landscape looks unnatural and weird.

 改造后的景观看起来很不自然，极其怪异

(2)adj.不自然的；做作的

She gave him a bright, determined smile which seemed unnatural.

她对他开朗、坚定地一笑，但笑得有点不自然。

【3】impress

(1)vt.给…深刻印象;使钦佩

What impressed him most was their speed.

最令他佩服的是他们的速度。

Cannon's film impresses on many levels.

坎农的电影在很多方面令人印象深刻。

(2)vt.使铭记;使谨记

I had always impressed upon the children that if they worked hard they would succeed in life.

我总让孩子们牢记努力工作就会成功。

I've impressed upon them the need for more professionalism.

我已使他们深刻认识到提高专业素养的必要性。

I impressed on him what a huge honour he was being offered.

我让他铭记他当时被授予了多么大的荣誉。

(3)vt.使…注意到;给…留下印象

But this change has not yet impressed itself on the minds of the British public. 但这一变化还没有引起英国公众的注意。

(4)vt.给…留下(…的)印象

Billy Sullivan had impressed me as a fine man.

比利·沙利文给我留下的印象是他是个很不错的人。

【4】describe ...as... 把…说成;把…称为;认为

He described it as an extraordinarily tangled and complicated tale.

他说那是一个非常曲折复杂的故事。

Eriksson described him as 'the best player on the pitch'.

埃里克森称他是“场上最好的球员”。

Andrew describes her as a large, bony and masculine woman.

安德鲁说她是一个瘦骨嶙峋、男人模样的大块头女人。

Even his closest allies describe him as forceful, aggressive and determined.

即使他最亲密的盟友也认为他强硬决断、咄咄逼人，不达目的誓不罢休。

He described the meeting as marking a new stage in the peace process.

他称这次会议标志着和平进程进入了一个新阶段。