The plow is to the agricultural system as the is to the industrial society.

steam engine

domestication of plants and animals

computer chip

unmapping of the dna molecule

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.