Subject-verb agreement

Hi.

Any help with the following would be most welcome

1) 'Globalisation is not a single process but a set of processes that operate simultaneously and unevenly on several levels.'

I keep thinking that 'operate' should be 'operates' because of the word 'set'

2) 'As we will see in subsequent chapters, the advocates of the first approach have marhalled impressive evidence for their view that the dramatic expansion and acceleration of global exhanges since the early 1970s represents a quantum leap in the history of globalisation.'

Would I be correct in saying that 'represents' instead of represent is determined by the words in italics and the italic phrase is being treated as one thing? What would happen if I were to remove the word 'dramatic'? Would it be possible to argue that 'represents' should be replaced by 'represent'?

3) 'Declining sales were responsible for the closing of the shop.'

Am I right in using 'were' instead of 'was'?

4) 'The decline of sales was the reason for the closure of the shop.'

Here I've used 'was' because I feel that decline is the noun

5) 'A decline of students is responsible for the university closing'

Similar reason to (4.

Thanks for all your help!