Answer:
The Steam Engine
Reasoning:
The plow was used to allow the plowing of fields to produce agricultural, it was an ends to a means; a tool.
The Steam engine was also just like that; It was a tool. The steam engine allowed us to import/export things from long distances, build new technologies with steam engine manufacturing.
Both technologies greatly helped push the human race to the next age.
Breaking down the choices:
The domestication of plants and animals happened long before the industrial age, even before the creation of the U.S.A! So this answer is wrong.
The computer chip is a creation of the "Information age", an age that is newer than the industrial age. So this answer is wrong.
The unmapping of the DNA molecule is also incorrect.
