The energy stored in rocks can cause vibrations as the rocks return to their original state. a) chemically b) mechanically c) thermally d) elastically

the answer is D. Elastically

d. new methods of assembly are introduced.

explanation:

this allows for the goods to be made on a larger scale. not faster because now it is shown to be made better, hence the greater productivity in the question. it is calling for something new to be introduced.

it sounds like either a or c