Question

Complete each sentence below with the correct form of ser or estar. La clase ____________________ aburrida.

Answer 1

I think it depends on what you mean by 'la clase'. 

La clase (in which 'clase' refers to the actual class itself) es aburrida.
La clase (in which 'clase' refers to the students in the class ) está aburrida.

I think the answer you are looking for is one of the two above. Hope this helps!

Answer 2

La clase es aburrida.