If I want to ask about some notion mentioning it in plural? Should I use "is" or "are"?
What is coroutines?
What are coroutines?
or better avoid such a forms and be strightforward
What is coroutine?
Intuitively I use "is" like it single notion which just described as word in plural form. But is there a rule for such a case? Or what the form is preferable?