I believe the answer is C. Both A and B.
        
             
        
        
        
Not only should the children should be taking care of the Grandparents. Everyone should be taking care of everyone. That's how family works. They should be because, the Grandparents would (should) do the same.
        
                    
             
        
        
        
A. terribly boring
This is probably just a shorter version of the word “excruciating.”