Is or Are (Visiting customers and listening to them is/are the basis for...)


Please read the following sentence:

Visiting customers and listening to them is / are the basis for (the) improvement of products or creating new ones.

Please correct the above sentence.

( Should I use “is” or “are” ? Can I remove “the” ? What is the differences beetween “for improvement of products” and “for the improvement of products” ?)



I think it fine to use both of is and are. But it depends.

My mom passed away, and at the very moment any sympathy and cooperation [color=green]is/are needed. (Take the sympathy and the cooperation as one, meaning if I got your sympathy, then I got your cooperation, if I got your cooperation, then I got your sympathy.)

Reading and swimming [color=green]are needed for a student. (not ‘is’ here since reading and swimming are totally two different things talked about.)