Nafta can be defined as
a means to acquire convenient resources.
a unification treaty that limits trade barriers.
an agreement between bordering nations.
a way for corporations to more easily outsource labor.

An agreement between bordering nations.

Explanation:

The North American Trade-Agreement, commonly known as NAFTA, is a trade agreement between bordering nations (Canada, United States and Mexico) that eliminates trade barriers, reduces tariff on imports and exports, increases investment opportunities by providing equal treatment to investors of the three countries, and establishes procedures to solve disputes.

It became effective on 1994, following thethe CFTA which didn't include Mexico. In 2018 NAFTA was renegotiated and the new trade agreement is now called the United States-Mexico-Canada agreement, which needs to be ratified before 2020.

lying without the limits of the several states; and may permit them, at such times, and in such manner as it

d) a constitutional amendment