There could be many answers such as: computer, tv, hair products/accessories, couches, tables, a stereo, video games
In this case, it could mean a site or receptacle where something may be stored.
They would have survived if they had been more ratical
The subordinate clause here is A, "as the layers of ash slowly compressed". Subordinate means that it cannot exist on its own, it has to be a part of the main, independent clause.
