Climate change is thus a prime example of what people have called a "social ecological system" with factors from different domains interacting on different spatial and temporal scales.
The above sentence is a part of an exercise in my English course. I was asked to change this sentence to passive voice. So, I made it like this.. Climate change is thus a prime example of what has been called a "social ecological system"...
My question is what is the function of what (after a prime example of...) in this sentence? Is it a subject of noun clause or is it a pronoun of social ecological system? This is really confusing to me. Please help explain.
Thank you so much.