Hello. 1.a. Many years ago, psychologists performed an experiment in which they put a number of people in a room, alone except for a ring toss set. It was one of those children’s toys with a short wooden post held upright on the floor and a bunch of round rings. (from Korean university entrance exam) I think that 'alone' modifies 'room' and 'alone except for a ring toss set' is essential. If so, why is 'comma' used before 'alone'? Is 'alone except for a ring toss set' non-essential? Thank you always~.