【问题征答】请各位老师分析下列句子成分，尽量全面详尽，并找出相似的结构及例句。

I'm at a loss which to choose.（为下面宾语从句简化版）

=I'm at a loss which I should choose（以结构完整宾语从句形式）

(1) at a loss 茫然， 不知所措; 亏本; 困惑; 神思恍惚;

be +（介词短语at a loss）=be +（分词形容词confused）

I'm at a loss which to choose.

=I'm confused which to choose.

=I'm confused which I should choose.

句子结构为：主语+系动词+介词短语(表语）+(疑问词+不定式to do 结构构成的一个短语） (备注：这种英语句子的语言现象在英语语法界没有一个统一定性分析和语法命名。只能从类似其它传统英语句子结构进行相似似性的语法结构分析。）

以上结构实际上是：主语+系动词+表语+从句结构的一个简化形式

Mary is at a loss what to do next.  

玛丽不知道下一步该做什么.

I'm at a loss how to do with it.
我不知道怎样处理这件事情。

He is always at a loss what to say in front of strangers.
他在生人面前总是不知要说什么

They are at a loss when to hold the meeting .

She is not at a loss what to say at a meeting.

We are at a loss where to find the financial aid.

She is at loss which book to read first.

主语+系动词+介词短语(表语）+(疑问词+to do) 结构中，疑问词to do可以从以下几语法理论分析(备注：这种英语句子的语言现象在英语语法界没有一个统一的定性分析和语法命名。只能从类似其它传统英语句子结构进行相似似性的分析。）

(1) 分析表语宾语成分/介词宾语成分

（把”系动词+表语“看作整体作句子谓语成分，后面作宾语成分）

(2)分析为状语成分

（把“系动词+表语”看作谓语，后面从句起着修饰谓语作用，即作状语。）

There are so many designs that I'm at a loss whichto choose.

款式如此之多,我不知该选哪个。

There are five pairs to choose from, but I'm at a loss which to choose.

有五双可供选择,但是我拿不定主意从中选择哪一双。

We are at loss in regard to this awkward situation.

现在的情势有些不尴不尬，大家都很茫然。

I am in two minds about which to choose.

我决定不了挑选哪个好。

He was at a loss how to cut the knot.

他不知如何才能大刀阔斧地解决这一难题。

最后我总结以下我个人一点不成熟看法，不一定正确，如有不妥当之处，或者错误，请提出并指正，谢谢！

对于英语初学者来说，只需要知道以下几点就可以了。

(1)疑问词+to do 结构 相当于疑问词的宾语从句简化形式

I am at a loss which to choose（简化版）

=I am at a loss which I should choose.（完整宾语从句）

(2)疑问词+to do 结构可以放在动词后/介词后/形容词后作宾语

A:动词宾语

I can't decide which to choose.（动词宾语）

 We must know what to say at a meeting. 
 He could not tell whom to trust. 
Do you know how to play bridge?

B:介词宾语

Can you give an idea on which to choose.

C:形容词宾语

I am confused which to choose.

He' s doubtful (about) which to choose.

Jim is not sure whose to choose. 
 Mary and John are not certain whether to get married or not.

(3)疑问词+to do 结构 放在谓语动词前/系动词前作主语

When to hold the meeting has not yet been decided. 
Where to live is a problem. 
How to cope with the rising cost of living becomes a daily discussion topic.

(4)疑问词+to do 结构放在系动词后作表语

The problem is where to find the financial aid. 
The question is who to elect.

The question is which to choose.

(5) 疑问词+to do 结构放在抽象名词后作同位语

Tom had no idea which book to read first. 

Do you have a rough impression how to do it?