The construction is:

'Beans are an ideal substitute for meat.'

Two with plural subject and singular object:

"Cash transfer payments are an ideal substitute for earned income."

"Soap Flakes are an ideal substitute for washing powder when used for delicate fabrics or sensitive skin."


Example of singular subject/verb and plural object:

"The CaC03 whisker is a new kind of microfibre, with high strength and durability, which is an ideal substitute for traditional fibres."

Hi Clare,

Thank you for your reply!

So it seems that Two with plural subject and singular object

&

singular subject/verb and plural object are both correct?

And subject and object do not always need to be in the same form right? (plural or singular)

But Why 'A bean is an ideal substitute for meat.' is incorrect? since A+noun can be used to express a type of things? (I could tell from my experience that it is a bit weird but just don't understand why honestly...)

Another example:
Classrooms are locations for children to study.
Classrooms are the best location for children to study.

Both are correct? (Coz what I need to pay attention is to keep subject in line with the verb, and subject and object doesn't really matter?)

Hope there are not too many questions

Thanks!
Ashley