I want to ask you the question which actually already is explained by the link below
Inverse copular constructions where the inverted predicative expression is a noun phrase are noteworthy in part because subject-verb agreement can (at least in English) be established with the pre-verb predicative NP as opposed to with the post-verb subject NP, e.g.
a. The pictures are a problem. - Canonical word order, standard subject-verb agreement
b. A problem is/??are the pictures. - Inverse copular construction, subject-verb agreement reversed in a sense
a. Those kids are an annoyance. - Canonical word order, standard subject-verb agreement
b. An annoyance is/??are those kids. - Inverse copular construction, subject-verb agreement reversed in a sense
In the inverse copular constructions, the copula agrees with the singular predicative expression to its left as opposed to with the plural subject to its right. Interestingly, this phenomenon seems to be limited to English (and possibly French); it does not occur in related languages such as German, e.g.
a. Die Bilder sind ein Problem. - Canonical subject-verb agreement
'The pictures are a problem.'
b. Ein Problem sind/*ist die Bilder. - Plural agreement with inverted subject maintained
'A problem are/is the pictures.'
Nor does it occur in some Romance languages, e.g. Italian:
a. Queste foto sono la causa della rivolta. - Canonical subject-verb agreement
'These photos are the cause of the revolt.'
b. La causa della rivolta sono/*è queste foto. - Plural agreement with inverted subject maintained
'The cause of the revolt are/is the photos.'
The fact that English (unlike German and Italian) demands subject-verb agreement to occur with the pre-verb NP generates confusion about what should qualify as the subject NP. From a morphological point of view, the pre-verb NP in inverse copular constructions should count as the subject, but from the perspective of information structure (e.g. definiteness, old information, specificity), the post-verb NP should be the subject.
The question is: Can I or cannot use phrase like, a problem are the pictures?
This question came to my mind after this theme:
http://www.englishclub.com/esl-forums/viewtopic.php?f=199&t=72967 , but I cannot ask my question in that theme becouse it's closed.