I came across this sentence online:
C extensions are a big part of the Ruby ecosystem.
Now, the word "C extensions" is the subject of the sentence and it's in plural form. The writer wants to say that the ability to write extensions in C (a popular programming language!) is a major part of programming practices inside Ruby (another programming language) environment. With this meaning in mind, is it correct to use the plural auxiliary 'are' to refer to a subject, although in plural form, functions as one unit or as a whole?!
If I were to write the same sentence, I would probably say:
C extensions is a big part of the Ruby ecosystem.