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.
New/fresh. A spring gives out fresh, new water. A spring bounces back with new, reversed energy. Plants grow and sprout in the Spring.
The answer for this is A. I didn’t watch it but someone told me about it
Depends on how major or minor the errors are. If the errors are due to lack of knowledge then it isn't a sign of progress but if less errors are being made and they are small ones progress may be shown.